CHAPTER I
THE POCKET LENS, THE DISSECTING MICROSCOPE, AND SOME SIMPLE APPLIANCES

The object of this little book is to show how much may be seen with an ordinary pocket lens, and with a simple microscope; and, as far as possible, to dispel the idea, far too common, especially among beginners, that no real work can be done unless one has a compound microscope, with a large battery of lenses and an array of ‘accessories.’

It would be easy to multiply quotations, from high authorities, in support of the proposition implied in the foregoing paragraph. Two only must suffice.

In a recent review of a very good book dealing with Butterflies and Moths (Natural Science, vol. vi. p. 293), the following passage occurs: ‘The only suggestion we should like to make is that a compound microscope is unnecessary for any of the details that the author mentions. A first-rate platyscopic hand lens is much more convenient and the young naturalist should train himself thoroughly in the use of it. There is no more common error than the undue use of the higher powers of a microscope. Except for the intimate details of histology, a low power or a hand lens is much more easy to use, and its employment gives a much better idea of the structure.’

The next quotation is of greater interest, as it gives some insight into the way in which Darwin carried on his investigations. In the Life and Letters of Charles Darwin (vol. i. pp. 145, 146) we are told: ‘His natural tendency was to use simple methods and few instruments. The use of the compound microscope has much increased since his youth, and this at the expense of the simple one. It strikes us nowadays as extraordinary that he should have had no compound microscope when he went his Beagle voyage; but in this he followed the advice of Robert Brown, who was an authority in such matters. He always had a great liking for the simple microscope, and maintained that nowadays it was too much neglected, and that one ought always to see as much as possible with the simple before taking to the compound microscope. In one of his letters he speaks on this point, and remarks that he always suspects the work of a man who never uses the simple microscope.’

It may be well here to verify the quotations, and also to consult Darwin’s Naturalist’s Voyage, to ascertain what kind of objects he examined with the simple appliances at his command. In the first chapter there is an interesting account of a curious limy deposit on the rocks of the island of St. Paul’s, and of the discoloration by confervae of the water, which, ‘under a weak lens, seemed as if covered by chopped bits of hay, with their ends jagged.’ Then we have an account of the confervae in the Indian Ocean, and of infusoria so numerous as to tinge the water off the coast of Chile. In the second chapter we have observations and experiments on planarian worms. ‘Having cut one of them transversely into two nearly equal parts, in the course of a fortnight both had the shape of perfect animals.’ In the next chapter he records some observations on the structure of vitrified tubes formed by lightning striking loose sand. In the fifth chapter is an elaborate description of a kind of sea-pen; and in the ninth chapter there are some remarks on the vast number of eggs in the egg-ribbon of a sea-slug, and on the ‘bird’s-head’ organs in certain Polyzoa. These remarks were, of course, founded on actual inspection with the simple microscope.

To this instrument, also, we owe the discovery of the tadpole-like larvae of Ascidians, or Tunicates, as they are now generally called. ‘At the Falkland Islands I had the satisfaction of seeing, in April, 1833, and therefore some years before any other naturalist, the locomotive larvae of a compound ascidian.... The tail was about five times as long as the oblong head, and terminated in a very fine filament. It was, as sketched by me under a simple microscope, plainly divided by transverse opaque partitions, which I presume represent the great cells figured by Kovalevsky. At an early stage of development the tail was closely coiled round the head of the larva[1].’

We come now to our pocket lens, which may be purchased for a few shillings of any optician. One can buy a serviceable single lens, in an ebonite handle, for a shilling; and this cheap instrument is sufficiently powerful not only to give the worker a good general idea of the form and structure of objects, but to enable him to do real work. With it the habits of many of the inmates of his aquaria may conveniently be watched; he may see their development from stage to stage of their life-history; and with it, when they are broken up, he may make out a good deal of their external and internal anatomy.

A very good form is shown at Fig. 1, which represents a hand magnifier, fitted with three lenses of different focus, generally 2 in., 1½ in., and 1 in. Examination of the catalogues of the principal London opticians shows that such a set of lenses may be bought for about 3s. In shape and construction there is sometimes a little variation; but the form figured is that most generally adopted, and is, on the whole, fairly convenient. It would, however, be an advantage if the hole by which the magnifier is mounted on the stand were drilled in the solid part of the handle. This would not only do away with the objection that the hole in the case permits dust to penetrate to the glasses, when carried in the pocket, but would give a longer reach, and thus obviate the necessity for moving the stand if the observer were examining a large object. The price of the stand figured is 2s. 6d.; and one with a short adjusting arm ought not to cost much more.

Any one with a mechanical turn may make a stand for himself, though it may be doubted whether this is quite worth while when these articles may be bought so cheaply. Nevertheless, there is great pleasure in making things for oneself; and a home-made stand will enable the observer to do quite as good work as one that came from the optician’s shop.

A bill-file weighted at the foot may be bought for a few pence, and adapted to the purpose. For the slider a large cork cleanly pierced will answer admirably. This should carry a piece of stout wire, bent at the end thus __ , to serve as a holder for the magnifier, which should have a hole in the handle, for the reasons stated above. The only difficulty will be the attachment of the wire to the cork. The Rev. J. G. Wood advocated winding the wire round the cork in a spiral; and this is a very good plan. An increase of steadiness is secured, if a larger cork, or small bung, be used, and the wire inserted in the side.

There are, of course, more expensive lenses, with which better definition can be obtained. Zeiss has an excellent magnifier consisting of two lenses, for use in the dissecting microscope (Fig. 2), and also as a hand lens, at the price of 6s.; one of the same construction, for use in the dissecting microscope alone, may be had for 4s. The Steinheil achromatic lenses are probably the best of all. These are made in powers ranging from 2 in. to ½ in. focus[2]; and the price varies from 10s. up to £1, according to the maker. Those made by Leitz of Wetzlar cannot be surpassed; and they are sold in London at 10s. each, either mounted in a handle, for use as hand magnifiers, or with a collar for use in Leitz’s dissecting microscope (Fig. 3). Mr. Lewis Wright says that ‘the best plan is to combine both uses, and have two or three powers in collars, with a spring ring folding into a handle, which will carry any one of them in that manner. A Steinheil lens at this low price costs little more than a Coddington, while its performance is infinitely superior[3].’ It is a difficult thing to get makers to deviate from the beaten track, and so far as I have been able to learn, Mr. Wright’s wishes have not been fulfilled.

The lenses and stand (Fig. 1) constitute a simple form of dissecting microscope. If the worker wishes for something more elaborate, he need only consult the catalogues of the principal makers to find something that will meet his requirements. Zeiss’s brass stand, with stage, above which a lens slides up and down in a holder (Fig. 2), is sold for 9s.; with blocks for supporting the hands, at 10s. It is a useful instrument for small objects.

My favourite instrument is shown at Fig. 3. Here the focussing of the lens is effected by rack and pinion work, by means of the screws on each side the upright pillar. The lens is shown fitted in the collar which carries it. The stage is of glass—roughly, 2½ in. long by 2 in. wide, and the arm at the top of the pillar can be moved from side to side, so as to bring a fairly large object within range. The metal framework of the stage is furnished with nickelled clips (not shown), which serve to hold an excavated slip. The arm-rests are detachable, and the uprights are hinged for convenience of packing. The instrument (with the exception of these rests) packs into a neat, strong mahogany box, 7½ in. in length, and about 5 in. in height and width. With two powers—1 in. and ½ in. are very serviceable ones—the cost is 38s.

It is to be wished that the maker would devise some plan by which the admirable lenses sold with this instrument could be utilized for the pocket. Mr. C. Curties, of Baker & Co., High Holborn, has kindly done something in the matter, and has made for me a metal holder. I have found this convenient, but should be glad to see something further done in the same direction, so that instrument, lenses, and holder could be sold for £2. This ought to be within the range of practical optics. The spring collar advocated by my friend Mr. Wright seems better, and would certainly be cheaper. The lenses would only need to be dropped in. To use my pocket holder one must unscrew the metal collar from the lenses before screwing them into the metal plates which carry them (Fig. 4). It is, however, something to have made a beginning: it is a step in the right direction.

A serviceable dissecting microscope—not a toy, but an instrument with which real work may be done—can be made at a cost of a few shillings. Such a one has been made for me by a friend with a positive genius for such work. The body is fashioned out of a parcel-post box 7 in. long, 3½ in. in height, and the same in width. From the centre of the sliding top a piece is cut away, leaving ledges to take a 3 in. by 1 in. excavated slip for small dissections, or a mounted slide of a large object, such as a whole insect, for examination. A further portion is cut away on each side to take a small dissecting dish (Fig. 6). To admit the light, a hole is cut in the side of the box; and the mirror consists of a piece of silvered glass which was bought of a hawker in the street. This is placed in the box opposite the square hole, and sloped at an angle of 45°. The aid of a skilled mechanic was sought for a small rod carrying a thread, which works in a piece of brass bent at a right angle. This piece of brass is screwed on the box, just above the aperture by which light is admitted, and carries a pocket magnifier, similar to that shown at Fig. 1.

This modest little instrument generally stands on my work-table, and has provoked some remark and a little good-natured banter from friends who have seen it. Nevertheless, I should be sorry to part with it, for I have found it extremely serviceable in many ways. And more than one critic has had to confess that better results were obtained than one would expect from its appearance. The total cost out of pocket was, 3d. for the box, 3s. for the lens, and 1d. for the plate-glass, while the man who made the pillar and ear-piece would take no more than 6d. for his work. This brings the total to 3s. 10d. With a little ingenuity the pillar might be made to carry a collar, and so take a Steinheil lens. This would swell the total cost to about 11s.

Other apparatus need not be costly. An incident occurred at the meeting of the Quekett Microscopical Club on November 22, 1878, which shows how readily common objects may be utilized for our purpose. The late Right Hon. T. H. Huxley, who was at that time President, exhibited, and made some remarks on, the dissecting microscope which now bears his name. During the discussion which followed, Professor Charles Stewart exhibited some little saucers, which were admirably adapted for dissecting purposes. The President said that he should ‘be glad to know where these convenient little saucers could be obtained.’ The next paragraph of the minutes is interesting and instructive. ‘Mr. Stewart said they were to be found at the corners of the streets, containing three whelks or three mussels for a penny. He bought those he had brought to the meeting at a shop in the New Cut, where they were supplied to costermongers[4].’

As very many of the objects with which we are concerned are aquatic, we shall want vessels of some sort to serve as aquaria. Any glass vessel will answer our purpose, provided it is clear, to allow of the examination of our captives; or shallow pie-dishes may be utilized. The glass pots in which preserves are sold will do admirably, and any glazier will cut us covers for a few pence. Within reasonable limits, the smaller the aquaria are the better. The inmates can be seen more easily, and picked out with less trouble when one wishes to examine them.

The principles on which aquaria should be kept are now pretty generally understood. There should always be a small quantity of growing aquatic vegetation, and a supply of minute life to furnish food for the larger forms. Excess of light should be avoided, and the temperature should not be allowed to rise much above 50° F. Carnivorous beetles and their larvae may be fed with small pieces of meat, small garden worms, or tadpoles. Most of the smaller larvae treated of will be satisfied with vegetarian diet, varied with an occasional meal of water-fleas.

If one cannot lay the household stores under contribution for jam-pots, tumblers, and bottles, beakers (Fig. 7) make capital small aquaria. They are sold in nests, and may be had either rimmed or lipped—rimmed for choice. There is no difficulty in obtaining them of any optician or glass-merchant. Mine have been bought from Messrs. Beck, of Cornhill, as have the capsules, &c., figured here.

Glass capsules (Fig. 8) are made in different sizes, ranging from 1½ in. to 3 in. in diameter, with a height of 1 in. or 2 in. The largest size, 3 in. by 2 in., costs 5d., and a glass circle to cover it, 1d. These capsules will be found useful for small aquaria, and for isolating aquatic larvae in order to keep them under observation during their change to perfect insects. It was in a capsule of this kind that some of my Ptychoptera larvae (p. 184) were kept, and changed into the pupal condition.

The glass block, with cover (Fig. 9), is convenient for a number of purposes. In it small creatures may be examined in air or in water, and it makes an exceedingly convenient little dissecting dish for use with the mounted hand magnifier (Fig. 1), or with Leitz’s stand (Fig. 3), or the home-made stand (Fig. 6). The glass box, with cover (Fig. 10), is extremely good for keeping small creatures under observation.

Excavated glass slips, 3 in. by 1 in., may be bought from any optician. They serve for the examination of objects in water, and also for dissection. The best I have been able to get have been supplied by Mr. J. Hornell, of the Biological Laboratory, Jersey, and they are very cheap.

We shall need some forceps to pick up specimens from the vessels in which they are kept, and the same little instruments will be found convenient in collecting. Both forms have advantages of their own; if we are limited to one pair, they should be curved, and of brass. Forceps with ivory tips are very useful for handling aquatic vegetation. These articles are not usually sold by opticians, but are kept by the tradesmen in Clerkenwell who sell jewellers’ and watchmakers’ tools, and cost from 1s. to 1s. 6d. a pair.

Dipping-tubes are used to take up small aquatic animals from the vessels in which they are kept. Very little practice will render the use of this instrument easy. The tube is held firmly between the thumb and the third and fourth fingers of either hand, while the index finger is pressed firmly on the top. Most people naturally prefer the right hand, but it is well to accustom oneself to use the right or left indifferently. The open end is then put into the water, just over the object to be secured, and the index finger lifted. The rush of water into the tube will carry the object into it, and if the finger be again applied to the top, the pressure of the atmosphere will prevent the water from escaping when the tube is lifted out[5].

Small brushes are useful for taking up specimens from the water or from pickle; common ones will do very well for large objects, but for small objects and parts it is advisable to have one or two sable brushes, as these form a better point.

Some needles fixed in handles will also be necessary. These may be bought, or made by fixing ordinary needles of requisite sizes into the handles sold for small brushes. The needles must be kept free from rust, and should always be carefully wiped after use. A good plan to keep them clean is to stick them in a gallipot in which has been melted a mixture of lard and paraffin in equal proportions.

Small dissecting-knives are useful, but all the work described here may be done with an ordinary pocket-knife in good trim.

The best preservative for our purpose is formalin, which is sold in a forty per cent. solution. This should be treated as absolute, and a five per cent. solution made. This will really be a two per cent. solution, and is sufficiently strong for general use.

The most profitable use we can make of specimens is to watch their habits while living, and to break them up and learn as much as we can about their structure when they are dead. For us to make a collection of specimens in tubes would be a waste of material.

Little need be said about collecting. The objects treated of are so plentiful that no great skill, nor any wealth of appliances, is needed to secure an ample supply. The following remarks on the methods employed at the Illinois State Laboratory for the capture of aquatic insects and larvae are, however, worth quoting:—

‘Insects in vegetation, and on or in the bottom, were taken by means of a dip-net—a net of about equal depth and width attached to a strong semicircular ring, firmly fixed to a long handle, the straight side of the ring being opposite the point of attachment. For the larger and more active forms, a coarser net was used, and for smaller forms one made of finer net proved most durable and satisfactory. To collect from the mud of the bottom, the water immediately over it was violently stirred and then swept with the net. The surface layer of mud was also scooped up in the fine dip-net, and then allowed to wash through, leaving the coarser contents in the net. Insects on the bottom in deep water were secured by using a dredge, and washing its contents through net sieves. The aquatic vegetation, when free from mud, was violently washed in a large pan, many smaller forms being thus dislodged and coming to the surface. Insects occurring in open water were taken in drawing an ordinary towing-net[6].’

Here we have, so to speak, the general principles of collecting. It will be easy to adapt them to particular cases.

In choosing the subjects to be treated of in this little book, some difficulty has been experienced in deciding what to select from the multitude that lay ready to hand. It was felt necessary that the subjects should be connected, since choosing them at random would lead to purposeless work, and so to waste of time and opportunity. After some consideration, the author has decided to take all the examples from the Arthrop´oda—that great sub-kingdom of backboneless animals which includes the Lobster, the Crab, the Sand-hopper and the Woodlouse, the Spider and the Mite, the whole world of Insects and the Centipedes. One cogent reason that influenced this decision was the fact that these objects are exceedingly common, so that there can be no difficulty in procuring material on which to work. There is, perhaps, no other sub-kingdom so full of interest, on account of the many widely different forms, which may be referred to one common plan.

It may possibly appear to some readers that the powers of the pocket lens have been exaggerated. As a matter of fact the material for the book has been gathered by actual observation. The author has seen, with an ordinary pocket lens, the objects here described. If some are shown as they would appear under greater magnification than such a lens would give, this is chiefly for the sake of emphasizing points of interest which might otherwise be overlooked, but which can readily be made out with a hand magnifier, when attention has been drawn to them, and the observer knows what to look for.