Sometimes an animal changes color when its surroundings change. Certain hares and grouse of northern latitudes are white in winter when the snow covers all the ground, but in summer when much of the snow melts, revealing the brown and gray rocks and withered leaves, they put on a grayish and brownish coat of hair or feathers. A small insect called the toad-bug (Galgulus) lives abundantly on the banks of a pond on the campus of Stanford University. The shores of this pond are covered in some places with bits of bluish rock, in others with bits of reddish rock, and in still others with sand. Specimens of the toad-bug collected from the blue rocks are bluish or leaden in color, those from the red rocks are reddish, and those from the sand are sand-colored. Changes of color to suit the surroundings can be quickly made by some animals. The chameleons of the tropics change momentarily from green to brown, blackish, or golden. There is a little fish (Oligocottus snyderi) common in the tide-pools of the Bay of Monterey in California whose color changes quickly to harmonize with the rocks it happens to rest above. Such changing coloration to suit the surroundings may be called variable protective resemblance.
Very striking are those cases of protective resemblance in which the animal resembles in color and shape, sometimes in extraordinary detail, some particular object or part of its usual environment. This may be called special protective resemblance. The larvæ of the Geometrid moths called inch-worms or span-worms are twig-like in appearance, and have the habit, when disturbed, of standing out stiffly from the twig or branch on which they rest, so as to resemble in attitude as well as color and markings a short or broken twig. To increase this simulation the body of the larva often has a few irregular spots or humps resembling the scars left by fallen leaves, and it also lacks the middle prop-legs of the body common to other lepidopterous larvæ, which would tend to destroy the illusion so successfully carried out by it. The common twig-insect or walking-stick (fig. 162) with its wingless, greatly elongate, brown or greenish body and legs is when at rest quite indistinguishable from the twigs on which it lies. Another excellent example of special protective resemblance is furnished by the famous green-leaf insect (Phyllium) of the tropics, which has broad leaf-like wings and body of a bright green color with markings which imitate the leaf-veins, and small irregular yellowish spots which simulate decaying or stained or fungus-covered spots in the leaf. Most striking of all, however, is the large dead-leaf butterfly Kallima (fig. 163) of the East Indian region. The upper sides of the wing are dark with purplish and orange markings not at all resembling a dead leaf. But the butterflies when at rest hold their wings together over the back, so that only the under sides of them are exposed. These are exactly the color of a dry dead leaf with markings mimicking midrib and oblique veins, and, most remarkable of all, what are apparently two holes like those made in leaves by insects, but in the butterfly imitated by two small circular spots free from scales and hence clear and transparent. When Kallima alights it holds the wings in such position that the combination of all four produces with remarkable fidelity the simulation of a dead leaf still attached to the twig by a short pedicel or leaf-stalk (imitated by a short "tail" on the hind wings). The head and legs of the butterfly are concealed beneath the wings.
Fig. 163.—The dead-leaf butterfly, Kallima sp., a remarkable case of special protective resemblance. (From specimen.)
Warning colors, terrifying appearances, and mimicry.—While many animals are so colored as to harmonize with their habitual or usual environment, others on the contrary are very brightly colored and marked in such bizarre and striking pattern as to be conspicuous. There is no attempt at concealment; it is obvious that conspicuousness is the object sought or at least produced by the coloration. Animals like these, we shall find, are in almost all cases specially protected by special weapons of defence such as stings or poison-fangs, or by the secretion of an acrid, ill-tasting fluid in the body. Many caterpillars have been found, by observation in nature and by experiment, to be distasteful to insectivorous birds. Now it is obvious that it would be advantageous to these caterpillars to be readily recognized by birds. After a few trials the bird learns by experience to let these distasteful larvæ alone; their conspicuous markings serve as warning colors. The black-and-yellow-banded caterpillar of the common milkweed or monarch butterfly (Anosia plexippus) is a good example of such protection by a combination of distastefulness and warning coloration. The little lady-bird beetles are mostly distasteful to birds; they are brightly and conspicuously marked. Certain little Nicaraguan frogs have a bright livery of red and blue, in strong contrast to the dull concealing colors of other frogs in their region. By offering these little blue and red frogs to hens and ducks the naturalist Belt found that they are distasteful to the birds.
Fig. 164.—The larva of the pen-marked sphinx-moth, Sphinx chersis, showing terrifying attitude. (After Comstock.)
Certain animals which are without special means of defence and are not distasteful are yet so marked or shaped, and so behave as to present a threatening or terrifying appearance. The large green caterpillars of the sphinx-moths, the tomato- and tobacco-worms, are familiar examples, each larva having a sharp horn on the back of the next to last body-segment (fig. 164). When disturbed the caterpillar assumes a threatening attitude, and the horn seems to be an effective weapon of defence. As a matter of fact it is not at all a weapon of defence, being weak, not provided with poison, and altogether harmless.
But it would plainly be to the advantage of a defenceless animal, one without poison-fangs or sting and without an ill-tasting substance in its body, to be so marked and shaped as to mimic some other specially defended or inedible animal sufficiently to be mistaken for it and thus to escape attack. Such cases have been noted, especially among insects. This kind of protective resemblance may be called mimicry. A most striking case is that presented by the familiar monarch and viceroy butterflies (fig. 165). The monarch (Anosia plexippus) is perhaps the most abundant and widespread butterfly of our country. It is a fact well known to entomologists that it is distasteful to birds and is let alone by them. It is conspicuous, being large and chiefly red-brown in color. The viceroy (Basilarchia archippus), also red-brown and patterned almost exactly like the monarch, is not, as its appearance would seem to indicate, a very near relation of the latter, but on the contrary it belongs to a genus of butterflies all of which, except the viceroy and one other, are black and white in color and of different pattern from the monarch. The viceroy is not distasteful to birds, but by its extraordinary simulation or mimicking of the monarch it is not distinguished from it and so is not molested. In the tropics there have been discovered numerous examples of mimicry among insects. The members of two large families of butterflies (Danaidæ and Heliconidæ) are distasteful to birds and are mimicked by members of other butterfly families (especially the Pieridæ).
Fig. 165.—The monarch butterfly, Anosia plexippus (above), distasteful to birds, and the viceroy, Basilarchia archippus (below), which mimics it. (From specimens.)
Alluring coloration.—A few animals show what is called alluring coloration; that is, they display a color pattern so arranged as to resemble or mimic a flower or other lure, and thus entice to them other animals, their natural prey. Certain Brazilian fly-catching birds have a brilliantly colored crest which can be displayed in the shape of a flower-cup. The insects attracted by the false flower furnish the bird with food. In the tribe of fishes called the "anglers" or "fishing frogs," the front rays of the dorsal fin are prolonged in the shape of long slender filaments, the foremost and longest of which has a flattened and divided extremity. The angler conceals itself in the mud or in the cavities of a coral reef, and waves the filament back and forth. Small fish are attracted by the lure, mistaking it for worms writhing about. When they approach they are engulfed in the mouth of the angler, which in some species is of enormous size. One of these angler species is known to fishermen as the "all-mouth."
For a fuller account of protective resemblances and mimicry see Jordan and Kellogg's "Animal Life," pp. 201-223. For still more extended accounts see Poulton's "Colours of Animals," and Beddard's "Animal Coloration."
CHAPTER XXXII
THE DISTRIBUTION OF ANIMALS
Technical Note.—The larger aspects or phenomena of the distribution of animals over the earth on land and in sea cannot be studied personally in the field by the student, but many local features of distribution can be so observed and studied. The restriction of certain kinds of animals to certain kinds of habitat, the presence and character and effectiveness of barriers, some of the modes of distribution, the presence and successful life of introduced foreign species such as the black and brown rats, the English sparrow, the German and Asiatic cockroaches, the gradual change of range or distribution of certain kinds of animals through the influence of a change in environment (caused by man in cutting off forests, cultivating heretofore wild pastures, etc.) all offer favorable and profitable opportunities for personal observation.
An excellent and feasible piece of field-work in distribution is the making of a zoological survey of the locality in which the school is situated. A map of the locality should be made on a generous scale, which should include all prominent physical features of the region, such as streams, ponds, hills, woodlands, marshes, etc., and on this map should be indicated the places where the various animals of the local fauna occur. Some of the animal species will have a limited range, and the limits of this range should be shown. This map and faunal list can be added to and perfected by successive classes. For fuller discussions of the geographical distribution of animals see Jordan and Kellogg's "Animal Life," Beddard's "Zoogeography," Heilprin's "The Distribution of Animals," and Wallace's "Geographical Distribution."
Geographical distribution.—It is a matter of common knowledge with all of us that there are no wild lions or camels or kangaroos or monkeys or ostriches or nightingales in North America. Ostriches are found only in Africa and South America, kangaroos only in Australia, lions only in Asia and Africa. On the other hand there are no opossums in Europe or grizzly bears or rattlesnakes anywhere else in the world than in this country. That is, certain kinds of animals have a certain limited range of occurrence or distribution. It is obvious, too, that certain animals live only on land, while others live only in water, and of these latter some are restricted to the ocean, while others live only in fresh water. All of the facts regarding the dispersion or diffusion of animals on land and in water make up the science of the geographical distribution of animals, or, as it is sometimes called, zoogeography. Under this subject are included not only the facts of the present actual distribution or occurrence of animals over the world, but the facts concerning the reasons for this distribution, the modes of travel and dispersion, the character and influence of barriers to the spread, and the results, in the adaptation of old forms and the production of new forms, of the phenomena of distribution.
Just as maps are made to show graphically the facts of political geography, which concerns the position and extent of the various powers and States which claim the allegiance of the people, and the facts of physical geography, which concerns the physical character of the earth's surface, so maps are made to show the geographical distribution of animals. Because of the great numbers of animal species no one map can show the distribution of all species, but a series of maps of the world or of a continent or of a State or county or more limited region could be made (and many such have been made) showing the distribution of selected species. In a map of a limited locality, say of a few square miles, the occurrence and distribution of most of the commoner and more familiar animals can be shown, and each high school should possess such a map (see technical note at beginning of this chapter).
Laws of distribution.—The laws governing the distribution of animals over the earth's surface have been recently[20] expressed in a simple statement as follows: Every species of animal is found in every part of the earth unless (a) its individuals have been unable to reach this region on account of barriers of some sort; or (b) having reached it, the species is unable to maintain itself, through lack of capacity for adaptation, through severity of competition with other forms, or through destructive conditions of environment; or (c) having entered and maintained itself it has become so altered in the process of adaptation as to become a species distinct from the original type.
Modes of migration and distribution.—That animals should be continually trying to extend their range is obvious from what we know of their rapid increase by multiplication. In a region which can provide food for but one thousand wolves, there is a production each year of several times one thousand. These new wolves must struggle among themselves for food, or migrate, if possible, to new regions as yet not inhabited by wolves. The wolf's mode of migration or distribution is walking or running, and so with other mammals except the bats and aquatic forms. Birds and bats can fly, and can thus migrate more swiftly, farther, and over barriers which would stop mammals. Most insects can fly. Worms can only crawl and very slowly at that. Fishes can swim, but if they are in a landlocked sheet of water, they cannot go beyond its confines. Marine animals can migrate from ocean to ocean, and land animals from continent to continent unless checked by barriers (see next paragraph).
But besides such voluntary and independent modes of distribution long journeyings may be made involuntarily, or by a passive migration as it may be called. Parasites, for example, are carried by their hosts in all their travels; the tiny Tardigrada and Rotifera, which can be desiccated and yet restored to active life by coming again into water, are carried in the dried mud on the feet of birds or other animals. On floating objects in rivers or in ocean currents land-animals may be carried long distances. Man, the greatest traveller of all, is responsible for the widened distribution of many animals. Thus have come to us in ships from Europe the black and brown rats, the English sparrow, the Hessian fly, the commonest cockroaches of our houses and many other forms. And these animals have been carried involuntarily all over the United States in railway-cars and wagons.
Barriers to distribution.—As is indicated in the paragraph on the modes of migration, a considerable sheet of water is obviously a barrier to the further travelling of a walking or crawling land-animal, although no barrier to a winged form. Similarly a strip of land is a barrier to a strictly aquatic animal as a fish. Or a high fall in the stream may serve as an insuperable barrier, making it impossible for any fish below the fall to reach the upper part of the stream. Numerous cases of this kind are known in the Rocky Mountains and Sierra Nevada, where a stream may be well supplied with trout below a fall, and quite bare of these fish above the fall. In the Yosemite Valley in California trout live in the Merced River below the great Vernal and Nevada falls, but above these falls the Merced contains no trout. To fresh-water swimming animals salt water may be a barrier; thus some kinds of fresh-water fishes are limited to one of two near-by streams although the mouths of these streams empty near each other into the ocean. The amphibious batrachians, at home in fresh water and on land, are killed by contact with sea-water. Earthworms also are killed by salt water. Thus the narrowest ocean strait is as effective a barrier to these animals as a whole sea. High mountain ranges and broad deserts are barriers to many land-animals, partly because of the physical obstacles, partly because of the differences in temperature and in food-supply.
Temperature and climate (as distinct from temperature) and the ocean are the three great barriers when we consider the animal kingdom as a whole, and look for the causes which determine the chief zoogeographical divisions of the earth's surface. Most of the tropical animals cannot endure frost, hence the isothermal line of frost is a line across which few tropical animals venture. Most arctic animals are enfeebled by heat, and the isothermal line which marks off the region in which frost occurs the year round is another great zoogeographical boundary. But while these lines are limits for localized species, some animals, as birds, especially, keep within a relatively uniform temperature by migrations across these lines. It should be borne in mind that the gradual decrease in temperature met with in going north or south from the tropics is also met in the ascent of high mountains. The summits of lofty peaks, even in the tropics, are truly arctic in character; they are snow-covered, and the animals and plants on them are truly arctic. Thus in the ascent of a single mountain a whole series of life-zones from tropical to arctic can be traversed.
Climate, as distinct from temperature, establishes limits of distribution. The animals of Eastern North America accustomed to a humid atmosphere cannot live in the dry plains and deserts of the West. Closely associated with climate is the nature of the plant-growth covering the land; here are forests and luxuriant meadows, there are sparse tough grasses of the dry plateau. The limits of a special kind of plant-growth often are the limits of distribution of certain animals.
The third great barrier, the ocean, is perhaps the most obvious of all in its influence. It is only in rare cases that any land-animal can independently cross a great ocean. Thus the land-animals of Australia differ from those of all other countries, and those of Africa and South America have developed almost independently of one another. The ocean is, as already mentioned, also a barrier for fresh-water aquatic animals, and even marine fishes which live normally in shallow waters along the shore rarely venture across the great depths of mid-ocean.
The obstacles or barriers met with determine the limits of a species. Each species broadens its range as far as it can. It attempts unwittingly, through natural processes of increase, to overcome the obstacles of ocean or river, of mountain or plain, of woodland or prairie or desert, of cold or heat, of lack of food or abundance of enemies—whatever the barriers may be. The degree of hindrance offered by any barrier differs with the nature of the animal trying to pass it. That which forms an impassable obstacle to one species may be a great aid to the spread of another. "The river which blocks the monkey or the cat is the highway of the fish and turtle. The waterfall which limits the ascent of the trout is the chosen home of the ouzel."
Faunæ and zoogeographic areas.—The term fauna is applied to the animals of any region considered collectively. Thus the fauna of Illinois includes the entire list of animals found naturally in that State. The fauna of a schoolyard comprises all the animals found living naturally in the yard. The fauna of a pond includes all the animal inhabitants of the pond. (Flora is used similarly of all the plants in a given region.) The relation of one fauna to another depends on the character and effectiveness of the barriers between, and the physical character of the two regions. Thus the fauna of Illinois differs but little from that of Indiana or Iowa, because there are no barriers between the States, and they are alike physically. On the other hand the fauna of California differs much from that of the Eastern States because of the great barriers (the desert and the Sierra Nevada Mountains) which lie between it and these States, and because of the great differences in the physical and climatic conditions of the two regions.
The land-surface of the earth has been divided by zoogeographers into seven great realms of animal life, based on the distributional characters shown by these various regions. These realms are separated by barriers of which the chief are the presence of the sea and the occurrence of frost. These realms are named, from their geographical region, the Arctic, the North Temperate, the South American, the Indo-African, the Madagascar, the Patagonian, and the Australian. Of these the Australian alone is sharply defined. Most of the others are surrounded by a broad fringe of debatable ground that forms a transition to some other zone.
Habitat and species.—The habitat of a species of animal is the region in which it is found in a state of nature. It is currently believed that the habitat of any animal is the whole of that region for which it is best adapted. But this is not necessarily true. In fact in most cases it is not true. The trout naturally debarred from the rivers in Yellowstone Park by the waterfalls could live there well if the barrier could be passed. In the case of one stream it has been passed and the trout flourish above the fall. The success of the black and brown rats and the English sparrow in America, of the rabbit in Australia, of bumblebees and house-flies in New Zealand, all of which animals had a natural habitat not including these regions, but by artificial means have been carried over the barriers and into the new territory, prove that "habitat" is not necessarily coincident with "only fit region." Shad, striped bass, and catfish from the Potomac River have been introduced into and now thrive in the Sacramento River in California. In fact the whole work of the introduction and diffusion of valuable food-animals in territory not naturally included in the habitat of the species is based on our knowledge that the habitat of a species is often determined by physical barriers rather than by exclusive fitness of environment. Within the natural habitat the environment is fit for the species' existence, outside of it the environment may be fit.
But there occur numerous instances where a species successful in leaving its original habitat is unsuccessful in attempting to maintain itself on new ground. Man has introduced various animals from one country to another. The English sparrow (naturally debarred from this country by the ocean barrier), brought to America from Europe, has covered its new territory rapidly and maintains itself with brilliant success. But the nightingale, the starling and skylark which have been repeatedly introduced and set free are unable to maintain themselves here.
Species-extinguishing and species-forming.—Accompanying the constant slow migrating of species into new habitats and the constant slow changing of environment and conditions everywhere is to be seen a constant modification of the fauna of any region due to the inability of some species to maintain their ground, the predominating increase of others, and the modifying or adaptive changing of others into new forms. In 1544 the black rat of Europe was introduced into America and it soon crowded out the native rats, being in its turn crowded out by the European brown rat (the present common rat in buildings), introduced about 1775. Here we have the original native species unable to maintain itself in competition with introduced forms.
With a change of environing conditions, certain species are unable to maintain themselves. With the destruction of the forests going on in parts of our country the great host of wood-creatures, the bears, squirrels, the wood-birds and insects, can no longer maintain themselves, and grow rare and disappear. Man often also influences the status of a species by checking its increase either by actual slaughter, as with the bison and passenger-pigeon, or by making adverse changes in its environment, as by destroying forests, or putting the plains under cultivation.
In the discussion of "species-forming" (see p. 408) it was shown that adaptation may lead to the altering of species, and to the formation of new ones (under the influence of natural selection). With the gradual change of conditions, or with the facing of new conditions because of an unusual migration to or invasion of new territory, those individuals of the species exposed to the new conditions must adapt themselves in structure and habit in order to meet successfully the new demands. By the cumulative action of natural selection these adaptive changes are emphasized; and this emphasis may come to be so pronounced that the part of the species represented in this newly acquired territory, if isolated from the original stock, is so altered as to be quite distinct in appearance from the old. If these changed individuals are also physiologically distinct from the old stock, i.e. are unable to mate with them, a new species is established. As already mentioned, the peopling of islands from mainlands is an excellent and readily observable example of the phenomena referred to in the third law of distribution.
APPENDICES
EQUIPMENT AND METHODS
APPENDIX I
EQUIPMENT AND NOTES OF PUPILS
Equipment of pupils.—Each pupil should have a laboratory note-book of about 8 × 10 inches, opening at the end, in which both drawings and notes can be made. The paper should be unruled and of good quality (not too soft). Each pupil should have also instruments of his own as follows: scalpel, pair of small scissors, spring forceps, pair of dissecting-needles, small glass pipette, and paper of ribbon-pins for pinning out specimens. The cost of this outfit need not exceed $1.00. The laboratory should furnish him with a dissecting-dish and a dissecting-microscope, or at least a lens.
Laboratory drawings and notes.—Each pupil should make the drawings called for in the directions for the laboratory exercises. These drawings should be in outline, and put in by pencil; the lines may be inked over if preferred. Shading should be used sparingly, if at all. Each drawing and all the organs and animal parts represented in it should be fully named. See the anatomical plates in this book for example. With such complete "labelling," little note-taking need be done in connection with the dissections.
Notes should be made of any observations which cannot be represented in the drawings; for example, on the behavior of the living animals. All notes referring to matters of life-history should be dated.
Field-observations and notes.—Scattered through this book will be found numerous suggestions for student field-work, for the observation of the life-history and habits and conditions of animals in nature. As explained in the Preface, the initiation and direction of such work must be left to the teacher. But its importance both because of its instructiveness and its interest is great. Pupils should not only be incited to make individual observations whenever and wherever they can, but the teacher should make little field-excursions with the class or with parts of it at various times, to ponds or streams or woods, and "show things" to all. The life-history and feeding-habits of insects, the web-making of spiders, the flight, songs, nesting, and care of young of birds, the haunts of fishes, the development of frogs, toads, and salamanders, the home-building and feeding-habits of squirrels, mice, and other familiar mammals are all (as has been called attention to at proper places in the book) specially fit subjects for field-observation.
Each pupil should keep a field note-book, recording from day to day, under exact date, any observations he may make. Let the most trivial things be noted; when referred to later in connection with other notes they may not seem so trivial. The field note-book should be smaller than the laboratory note- and drawing-book, small enough to be carried in the pocket. Notes should be made on the spot of observation; do not wait to get home. Sketches, even rough ones, may be advantageously put into the book. Students with photographic cameras can do some very interesting and valuable field-work in making photographs of animals, their nests and favorite haunts. Such photographic work is very effectively used now in the illustration of books about animals and plants (see the reproductions of photographs in this book). If the class is making a collection the collecting notes or data made in the field-books of the different pupil collectors should all be transferred to a common "Notes on Collections" book kept by the whole class.
APPENDIX II
LABORATORY EQUIPMENT AND METHODS
Equipment of laboratory.—The equipment of the laboratory or classroom will, of necessity, depend upon the opportunities afforded the teacher by the school officers to provide such facilities as instruments, books, and charts. If dissections are to be seriously and properly made, however, some equipment is indispensable. Flat-topped tables, not over 30 inches high, a few compound microscopes (one is much better than none), as many simple lenses, or, far better, simple dissecting-microscopes, as there are students, dissecting-dishes, a pair of bone-clippers, one injecting-syringe, a bunch of bristles, water, a few simple reagents and some inexpensive glassware, as slides, cover-glasses, watch-crystals, and fruit- or battery-jars for live cages and aquaria, make up a sufficient equipment for good work. Much can be done with less, and perhaps a little more with some additional facilities.
The dissecting-pans should be of galvanized iron or tin, oblong, about 6 × 8 inches by 2 inches deep, with slightly flaring sides. If an iron wire be run around the margin, and the margin bent back over it, it will strengthen the dish, and make a broader and smoother edge for the hands to rest on. Diagonally across the dish, about one-fourth inch from the bottom, should run a thick wire. A layer of paraffin one-half inch thick should cover the bottom. It should be poured in melted, when the diagonal wire will be imbedded in it and will hold it in place. Acids must not be put into the pan.
The reagents necessary are alcohol of 95 per cent and 85 per cent, and formalin of 4 per cent (the formaldehyde sold by druggists is 40 per cent and should be diluted ten times with water), these for preserving material for dissection; chloroform for killing specimens; glycerin for making temporary microscopic mounts, and 20 per cent nitric acid for preparing specimens for study of the nervous system. In addition there will be needed the few other materials mentioned in the following paragraphs as necessary in the preparation of injecting-fluids, the staining of fresh tissue and preserving by special methods.
A list of reference books desirable in the laboratory is appended as a separate paragraph (see p. 454).
Collecting and preparing material for use in the laboratory.—As directions have been given in the "technical notes" scattered through the book for the collecting and preparing of all the various kinds of animals chosen as subjects of the laboratory exercises, it will only be necessary to give here directions for making certain special mixtures and for the special preparation of specimens by injection, etc. Specimens to be used for dissection should be kept in alcohol of 85 per cent or in formalin of 4 per cent. Alcohol is better for the earthworm, but for the other examples formalin is either better or as good, and as it is much cheaper it may well be chosen for the general preservative.
Methyl green, a stain used for coloring fresh tissues. Dissolve the methyl green powder in water, using about as much powder as the water will take up. Add a few drops of acetic acid.
Injecting-masses.—Injections are best made with preparations of French gelatine, but white glue will answer most purposes. For fine injection use a combination of the following: 1 part of a solution of gelatine, 1 part to 4 parts of water; 1 part of a saturated solution of lead acetate in water, and 1 part of a saturated solution of potassium bichromate in water. A mixture of these when hot gives a beautiful yellow injection-mass which, filtered, will pass through the finest capillaries. For different colorings use dry paints, which come in ultramarine blue, vermilion, and green. The gelatine should be thoroughly soaked before the coloring-matter is added. A mistake is generally made in using the injection-mass too thick. One part by weight of gelatine to six or even more parts of water is a good proportion. The gelatine as well as glue-masses should be made in a water-bath, which consists of one dish placed within another outer one containing warm water. The mass should be injected warm, not hot, after which the injected specimen is to be placed in cold water until the injecting-mass has set. Glue (the ordinary white kind) can be used for most injections just as the gelatine was used, but should not be so much diluted. All injection-masses should be filtered through a cloth before using.
Preparing skeletons.—In general, skeletons are best cleaned by boiling. After most of the flesh has been cut away the skeleton should be boiled in a soap solution until the remaining parts of the muscles are thoroughly softened. The soap solution is made of 2,000 c.c. of water, preferably distilled, 12 grams of saltpetre, and 75 grams of hard soap (white). Heat these until dissolved, then add 150 c.c. of strong ammonia. This stock solution is mixed with four or five parts of water, when the mixture is ready for use. The bones after boiling are rinsed in cold water, brushed and picked clean, then left to dry on a clean surface.
Preserving anatomical preparations.—Many specimens worth keeping will be found, and for them a solution known as Fischer's formula is suggested as good, especially for brains. Fischer's formula is made up as follows: 2,000 c.c. of water, 50 c.c. of formalin, 100 grams of sodium chloride, and 15 grams of zinc chloride. These are mixed together until thoroughly dissolved. Open preparations well before placing them in the liquid and use about twenty times the volume of the object to be preserved.
To keep fresh dissections.—For materials which are dissected fresh and must be kept over for several days in a fresh condition add a few drops of carbolic acid to the water which covers them. Carbolized water (2 per cent in water) will preserve a great many tissues for a long time. Hearts will remain for years in a supple condition in this solution.
Obtaining marine animals, microscopic preparations, etc.—For schools not on the seashore the marine animals such as starfishes, etc., which are to be dissected or examined as examples of the branches to which they belong must be obtained as preserved specimens from dealers in such supplies. Among such dealers on the Atlantic coast are the Marine Biological Laboratory, Woods Holl, Mass.; F. W. Walmsley, Academy of Natural Sciences, Philadelphia, Pa.; and H. H. and C. S. Brimley, Raleigh, N. C.; on the Pacific coast the Supply Department, Hopkins Seaside Laboratory, Stanford University, California. Ward's Natural Science Establishment, Rochester, N. Y., supplies almost any biological specimens asked for. This establishment furnishes already made dissections and sets illustrating life-history and metamorphosis. The few permanent microscopic preparations which are mentioned in the book as desirable to have can be made by the teacher if he has had any training in microscopical technic. If not, they may be bought cheaply of such dealers in natural history supplies as the Bausch & Lomb Optical Co., Rochester, N. Y.; the Kny-Scheerer Co., 17 Park Place, New York City; Queen & Co., 1010 Chestnut Street, Philadelphia, Pa., and numerous others. From these dealers also can be bought all of the laboratory supplies, such as lenses, slides, cover-glasses, dissecting-scalpels, scissors and needles, etc., mentioned in this book.
Reference books.—Throughout the preceding chapters exact references have been made to various books, as many of which as possible should be in the school-library. Some of these references have been made with special regard to the teacher, but most with special regard to the pupil. All of the books referred to are included in the following list. For the convenience of the prospective buyer, the names of the publishers and prices of the books are appended. In buying books, it is of course not necessary to order from the various publishers. A list of the books desired may be handed to any book-dealer, who will order them and who should in most cases be able to get them for a little less than publisher's list prices.
Baskett, J. N. The Story of the Birds. 1899, D. Appleton & Co. $0.65.
Beddard, Frank. Animal Coloration. 1892, Macmillan Co. $3.50.
---- Zoogeography. 1895, Macmillan Co. $1.60.
Bendire, Chas. Directions for Collecting, Preparing, and Preserving Birds' Eggs and Nests. Distributed by U. S. National Museum.
Bird Lore, an Illustrated Journal about Birds. Macmillan Co. $1.00 a year.
Cambridge Natural History, Vols. V (Peripatus), $4.00, VI (Insects), $3.50. Macmillan Co.
Chapman, Frank. Handbook of the Birds of Eastern North America. 1899. D. Appleton & Co. $3.00.
Comstock, J. H. Manual for the Study of Insects. 1897, Comstock Publishing Co. $3.75.
---- Insect Life. 1901, D. Appleton & Co. $1.50.
---- and Kellogg, V. L. Elements of Insect Anatomy. 1901, Comstock Publishing Co. $1.00.
Cooke, W. W. Bird Migration in the Mississippi Valley. Distributed by the Division of Biological Survey, U. S. Dept. Agric.
Cowan, T. W. Natural History of the Honey-bee. 1890, London: Houlston. 1s. 6d.
Coues, Elliott. Key to North American Birds. 1890, Estes and Lauriat. $7.50.
Darwin, Chas. The Formation of Vegetable Mold through the action of Worms. D. Appleton & Co. $1.50.
---- Origin of Species. 1896, Caldwell. $0.75.
---- The Structure and Distribution of Coral Reefs. D. Appleton & Co. $2.00.
---- Plants and Animals under Domestication. D. Appleton & Co.
Davie, Oliver. Methods in the Art of Taxidermy. 1894, Oliver Davie & Co., Columbus, O. $10 net.
Gage, S. H. Life History of the Toad. Teacher's Leaflets No. 9, April, 1898, prepared by College of Agriculture, Cornell University, Ithaca, N. Y.
Heilprin, A. The Distribution of Animals. 1886, D. Appleton & Co. $2.00.
Hodge, C. F. The Common Toad. Nature Study Leaflet, Biology Series No. 1. 1898, published by C. H. Hodge, Worcester, Mass.
Holland, W. J. The Butterfly Book. 1899, Doubleday and McClure Co. $3.00.
Hornaday, W. T. Taxidermy and Zoological Collecting. 1897, Chas. Scribner's Sons. $2.50 net.
Howell, W. H. Dissection of the Dog. 1889, Henry Holt & Co. $1.00.
Huxley, T. H. The Crayfish: an introduction to the Study of Zoology. D. Appleton & Co. $1.75.
Jordan, D. S. Manual of Vertebrate Animals of the Northern United States, 8th ed. 1899. A. C. McClurg & Co. $2.50.
---- and Evermann, B. W. Fishes of North and Middle America, 4 vols. 1898-1900, Distributed by U. S. National Museum.
---- and Kellogg, V. L. Animal Life. 1900, D. Appleton & Co. $1.20.
Lubbock, John. Ants, Bees, and Wasps. 1882. D. Appleton & Co. $2.00.
Marshall, H. M., and Hurst, C. H. Practical Biology, 5th ed. G. P. Putnam's Sons. $3.50.
Martin, H. W., and Moale, W. A. Handbook of Vertebrate Dissection, 3 parts. 1881, Macmillan Co.
Part 1. How to dissect a Chelonian (red-bellied slider terrapin);
Part 2. How to dissect a bird (pigeon);
Part 3. How to dissect a rodent (rat).
McCook, Henry. American Spiders and their Spinning Work, 3 vols. 1889-1893, H. C. McCook, Phila., Pa. $30.00.
Miall, L. C. The Natural History of Aquatic Insects. 1895, Macmillan Co. $1.75.
Parker, T. J. A Course of Instruction in Zootomy. 1884, Macmillan Co. $2.25.
---- Lessons in Elementary Biology. 1897, Macmillan Co. $2.65.
---- and Haswell, W. A. Textbook of Zoology, 2 vols. 1897, Macmillan Co. $9.00.
Peckham, George W. and E. J. On the Instincts and Habits of the Solitary Wasps. 1898, sold by Des Forges & Co., Milwaukee, Wis. $2.00.
Potts, E. Fresh-water Sponges. 1887, Phil. Acad. of Sciences.
Poulton, E. B. The Colors of Animals. 1890, D. Appleton & Co. $1.75.
Reighard, J. E., and Jennings, H. S. The Anatomy of the Cat. 1901, Henry Holt & Co. $4.00.
Ridgway, R. Directions for Collecting Birds. Distributed by U. S. National Museum.
Riverside Natural History, 6 vols. Houghton, Mifflin & Co. $30.00.
Romanes, Geo. Darwin and After Darwin, I. 1895-97, Open Court Publishing Co.
Scudder, S. H. The Life of a Butterfly. 1893, Henry Holt & Co. $1.00.
Van Beneden, E. Animal Parasites and Messmates. 1876, D. Appleton & Co. $1.50.
Wallace, A. R. The Geographical Distribution of Animals. 1876, Harper & Bros. $10.00.
Wallace, A. R. Island Life. 1881, Harper & Bros. $4.00.
APPENDIX III
REARING ANIMALS AND MAKING COLLECTIONS
Much good work in observing the behavior and life-history of some kinds of animals can be done by keeping them alive in the schoolroom under conditions simulating those to which they are exposed in nature. The growth and development of frogs and toads from egg to adult, as well as their feeding habits and general behavior, can all be observed in the schoolroom as explained in Chapter XII. Harmless snakes are easily kept in glass-covered boxes; snails and slugs are contented dwellers indoors; certain fish live well in small aquaria, and many other familiar forms can be kept alive under observation for a longer or shorter time. But from the ease with which they are obtained and cared for, the inexpensiveness of their live-cages, and the interesting character of their life-history and general habits, insects are, of all animals, the ones which specially commend themselves for the schoolroom menagerie. In the technical notes in the chapter (XXI) devoted to insects are numerous suggestions regarding the obtaining and care of certain kinds of insects which may be reared and studied to advantage in the schoolroom. In the following paragraphs are given directions for making the necessary live-cages and aquaria for these insects.
Live-cages and aquaria.—Prof. J. H. Comstock has so well described the making of simple and inexpensive cages and aquaria in his book, "Insect Life," that, with his permission, his account is quoted here.
Live-cages.—"A good home-made cage can be built by fitting a pane of glass into one side of an empty soap-box. A board, three or four inches wide, should be fastened below the glass so as to admit of a layer of soil being placed in the lower part of the cage, and the glass can be made to slide, so as to serve as a door (fig. 166). The glass should fit closely when shut, to prevent the escape of the insects.