A. Regarding the movement of the flagella in mature swarm-spores compare L. N. 22, p. 375; L. N. 26, pp. 31, 35; L. N. 41, p. 452, and L. N. 52, p. 170.
B. On the active vertical swimming movements of mature Radiolaria, especially the cause of sinking and rising, see L. N. 16, p. 134; L. N. 41, p. 443, and L. N. 52, pp. 97-102.
C. On the active horizontal creeping movements of mature Radiolaria on a firm ground, compare L. N. 12, p. 10, and L. N. 16, pp. 132-134.
D. Regarding the motion of social central capsules within the same cœnobium and the changes thus brought about in the structure of the calymma, see L. N. 16, pp. 119-127, and L. N. 52, pp. 75-82.
221. Contraction.—Motions, which are due to the contraction of individual portions and cause changes in volume or form, have been partly already spoken of under the head of locomotion (§ 220) and are partly connected with other functions. Examples may be seen in the contraction of the central capsule and of the calymma. A certain contraction of the central capsule is probably brought about by the myophanes, which arise by differentiation of the endoplasm and hence may assume different forms in the four legions. In the Spumellaria, where numerous radial fibrillæ run from the central nucleus to the capsule membrane (§ 77), the endoplasm is probably driven out evenly through all the pores of the capsule membrane by their simultaneous contraction, and hence the volume of the capsule is diminished in all directions. The Acantharia probably behave similarly, but are different, inasmuch as the number of their contractile radial fibrillæ is less, and special axial threads (§ 78) are already differentiated. In the Nassellaria it is probable that owing to the contraction of the divergent myophane fibrillæ in the podoconus the vertical axis of the latter is shortened, the opercular rods of the porochora are lifted, and the endoplasm driven out of its pores, so that the volume of the monaxon central capsule is diminished (§ 79). In the Phæodaria the same result is probably brought about by the contraction of the cortical myophane fibrillæ, which run meridionally along the inside of the capsule membrane from the apical to the basal pole of the vertical main axis, where they are inserted into the periphery of the astropyle; since the volume of the capsule is diminished by their contraction (their spheroidal figure becoming more nearly spherical) the endoplasm will be driven out through the proboscis of the astropyle. Whilst these contractions of the central capsule are largely due to differentiated muscle-like threads of endoplasm (myophanes), this appears to be but rarely the case with the contractions of the extracapsulum (e.g., the myophriscs of the Acanthometra, § 96). Most of the phenomena of contraction which can be observed in the calymma and pseudopodia depend upon exoplasmatic currents (§ 209).
222. Protection.—Of the utmost importance, both for the physiology and for the morphology of the Radiolaria are their manifold protective functions, which we now consider under the heading "protection." From the physiological point of view the consideration of the exposed situation in which the delicate, free-swimming Radiolarian organism lives, and the numerous dangers which beset it in the struggle for existence, would lead a priori to the expectation, that many special protective adaptations would be developed by natural selection. On the other hand, morphological experience shows us that this latter has been in action for immeasurable periods, and has gradually produced an abundance of the most remarkable protective modifications. Examples of these may be found in the formation of the voluminous calymma, as a gelatinous protective covering for the central capsule, and further, the formation of the capsule membrane itself, which separates the generative contents of the central capsule from the nutritive exoplasm. The phosphorescence of the central capsule, too (§ 223), may be regarded as a useful protective arrangement; as also the radiating of the numerous pseudopodia in all directions from the surface of the calymma; for they are of great significance to the well-being of the organism, both as sensory organs and as prehensile organs. By far the most important and most varied means for the actual defence of the soft body is to be seen in the endless modifications of the skeleton; first, in the production of the enclosing lattice-shells and projecting radial spines, but especially also in the very varied structure of the individual parts of the skeleton, and in the special differentiation of the small appendicular organs which grow out from it (hairs, thorns, spines, scales, spathillæ, anchors, &c.). Finally "mimicry" possesses a considerable significance among the different forms of adaptation which are to be observed in this class.
223. Phosphorescence.—Many Radiolarians shine in the dark, and their phosphorescence presents the same phenomena as that of other luminous marine organisms; it is increased by mechanical and chemical irritation, or renewed if already extinguished. The light is sometimes greenish, sometimes yellowish, and appears generally (if not always) to radiate from the intracapsular fatty spheres (§ 73). Thus these latter unite several functions, inasmuch as they serve, firstly, as reserve stores of nutriment, secondly, as hydrostatic apparatus, and thirdly, as luminous organs for the protection of the Radiolaria; probably the light acts by frightening other animals, for the phosphorescent animals are provided with spines, nettle-cells, poison glands or other defensive weapons. The production of the light depends probably, as in other phosphorescent organisms, upon the slow oxidation of the fat-globules, which combine with active oxygen in the presence of alkalis. Phosphorescence is very likely widely distributed among the Radiolaria.
The shining of the Radiolaria in the dark has been noticed by the earliest observers of the class (see L. N. 1, p. 163, L. N. 16, p. 2, and L. N. 52, pp. 136-139). In the winter of 1859 I observed the production of light in the case of many monozootic and polyzootic Radiolaria, but inadvertently omitted to record the fact in my Monograph. I made more accurate observations in the winter of 1866 at Lanzerote in the Canary Islands, and convinced myself the the light emanates from the central capsule, and in particular from the fat-globules contained in it. In most Polycyttaria (both Collosphærida and Sphærozoida), when each central capsule contains a large central oil-globule the light radiates from it. In Collozoum serpentinum (Pl. 3, figs. 2, 3) each cylindrical central capsule contains a row of luminous spherules like a string of beads. In Alacorys friderici (Pl. 65, fig. 1) the four-lobed central capsule contains four shining points. Karl Brandt has recently made more detailed communication on this point (L. N. 52, p. 137).
224. Sensation.—The general irritability which we ascribe to all organisms, and as the basis of which we regard the protoplasm, remains at an inferior stage of development in the Radiolaria. For although they are subject to various stimuli, and certainly possess a power of discrimination, special sensory organs are not differentiated; the peripheral portions of the protoplasm, and especially the pseudopodia, rather act both as organs of the different kinds of sensation and various modes of motion. That different Radiolaria have attained different degrees of development in this respect may be seen partly by direct observation of the reaction of the living organism towards various stimuli, and partly by the comparison of the different conditions of existence under which Radiolarians exist, both in the most various depths of the ocean and in all climatic zones (see note A). In general the Radiolaria seem to be sensitive to the following stimuli; (1) pressure (see note B); (2) temperature (see note C); (3) light (see note D); (4) chemical composition of the sea-water (see note E). The reaction towards these stimuli, corresponding to the sensation of pleasure or dislike which they call forth, is shown in various forms of motion of the protoplasm, changes in the currents in it, contraction of the central capsule, changes in the size, position, and form of the pseudopodia, changes in the volume of the calymma (by the evocation of water), &c. Among the sensory functions of the Radiolaria must be especially mentioned their remarkably developed perception of hydrostatic equilibrium (see note F), as well as their perception of distances, so clearly shown in the production of equal lattice-meshes and other regularly formed skeletal structures (see note G).
A. I can add but little to the communication which I made twenty-four years ago regarding sensation in the Radiolaria (L. N. 16, pp. 128-131). The most important point would be the great difference in irritability which must obtain between the pelagic, zonarial and abyssal Radiolaria, which may be assumed from a consideration of their very different conditions of existence as regards pressure, light, warmth, nutrition, &c. It is natural to suppose that the numerous abyssal Radiolaria, discovered by the Challenger, which live at great depths (2000 to 4500 fathoms) in complete darkness, in icy cold and under an enormous pressure, must have quite different sensations of pleasure from their pelagic relatives which live at the surface of the sea under an equatorial sun. Karl Brandt has recently added much to our knowledge regarding the special action of different vital conditions upon the various Polycyttaria and the degrees of their irritability (L. N. 52, pp. 113-132).
B. Regarding the sensation of pressure or sensation of touch of the Radiolaria and the various degrees of their mechanical irritability, see L. N. 16, p. 129; L. N. 41, p. 464.
C. Regarding the sensation of warmth or temperature-sense and its dependence upon different climatic relations, see L. N. 16, p. 129; L. N. 52, pp. 114-129.
D. Regarding the sensation of light, compare L. N. 16, p. 128; L. N. 42, p. 304; L. N. 52, pp. 102-104, 114.
E. Regarding the sense of taste of the Radiolaria or their peculiar sensitiveness towards the different chemical composition of the water, change in its salinity, presence of organic impurities, &c., see L. N. 16, p. 130; L. N. 52, pp. 103, 113. This chemical irritability seems to be the most highly developed sense in the Radiolaria, even more so than their mechanical irritability.
F. The perception of hydrostatic equilibrium among the Radiolaria is immediately visible from the position which their bodies, floating freely in the water, assume spontaneously, and from the symmetrical development of the skeleton, which by its gravitation necessitates a definite position. It may be assumed that the development of the various geometrical ground forms which correspond to a definite position of equilibrium, is the result of this particular kind of perception (compare §§ 40-45).
G. The plastic perception of distance of the pseudopodia is shown by the symmetry with which the forms composing the regular skeletal structures (e.g., the ordinary lattice-spheres with regular hexagonal meshes, the radial spines with equidistant branches) are excreted from the exoplasm. Both this form of sensation and the one first mentioned (note F) have hitherto received scarcely any attention, but are deserving of a thorough physiological investigation.
225. The Cell-Soul (Zellseele).—The common central vital principle, commonly called the "soul," which is considered to be the regulator of all vital functions, appears in the Radiolaria as in other Protista in its simplest form, as the cell-soul. By the continual activity of this central "psyche" all vital functions are maintained in unbroken action, and in uniform correlation. It is also probable that by it the stimulations which the peripheral portions of the cell receive from the outer world are first transmitted into true sensation, and that, on the other hand, the volition, which alone calls forth spontaneous movements, proceeds from it. The central capsule is most likely the sole organ of this cell-soul or central psychic organ, and the active portion may be either the endoplasm or the nucleus, or both. The central capsule may thus (apart from its function as a sporangium, § 215) be regarded as a simple ganglion cell, physiologically comparable to the nervous centre of the higher animals, whilst the exoplasm (sarcomatrix and pseudopodia) are to be compared to the peripheral nervous system and sense organs of the latter. The great simplicity of the functions of the cell-soul which appear in the Radiolaria, and the intimate connection of their different psychic activities, give to these unicellular Protista a special significance for the comprehension of the monistic elements of a natural psychology.
Regarding the theory of the cell-soul as the only psychological theory which is able to explain naturally the true nature of the life of the soul in all organisms as well as in man, see my address on cell-souls and soul-cells ("Zellseelen und Seelenzellen") in Gesammelte populäre Vorträge aus dem Gebiete der Entwickelungslehre, Heft 1, p. 143; Bonn, 1878.
226. Universal Marine Distribution.—Radiolaria occur in all the seas of the world, in all climatic zones and at all depths. Probably under normal conditions they always float freely in the water, whether their usual position be at the surface (pelagic), or at a certain depth (zonarial), or near to the bottom of the sea (abyssal). This appears both from numerous direct observations, as well as from conclusions which may be drawn from their organisation (and especially their promorphology) regarding their floating life (compare §§ 40-50, 219, 220). Hitherto no observation has been recorded, which justifies the assumption that Radiolaria live anywhere upon the bottom of the sea (on stones, Algæ, or other firm substances), either sessile or creeping. They perform the latter action, however, when they fall accidentally upon a firm basis or are accidentally placed upon it, but they seem normally always to float freely in the water with pseudopodia radiating in all directions. Active free-swimming movements are only met with in the case of the flagellate zoospores (§ 142). The development of Radiolaria in large masses is very remarkable (see note A), and in many parts of the ocean is so great that they play an important part in the economy of marine life, especially as food for other pelagic and abyssal animals (see note B). Medium salinity of the water seems to be most favourable to their development in masses, although it is not unknown in seas of high and low salinity (see note C). There are no Radiolaria in fresh water (see note D).
A. The development of Radiolaria takes place in many parts of the ocean in astonishingly large masses on the surface, in different strata, and near the bottom. The Collodaria (and especially the Sphærozoida) often cover the surface of the sea in millions, and form a shining layer, phosphorescent in the dark like the Noctilucæ, as I observed in 1859 in the Strait of Messina, in 1866 at the Canaries, and in 1881 in the Indian Ocean. Similar masses of Sphærozoum and Acanthometron were seen by Johannes Müller on the French and Ligurian coasts (L. N. 12), and John Murray found another in the Gulf Stream, off the Færöe Islands, from the surface to a depth of 600 fathoms; considerable masses of large Phæodaria live there also.
B. The alimentary canal of Medusæ, Salpæ, Crustacea, Pteropoda, and many other pelagic animals is a rich field for the discovery of Radiolaria, and many of the species hereinafter described are from such sources. Fossil coprolites too (e.g., those from the Jura) often contain many Polycystina.
C. Some Acantharia (Acanthometra) and Phæodaria (species of Mesocena and Dictyocha) live in the Baltic; I found their skeletons in the alimentary canal of Aurelia, Ascidians and Copepods.
D. The so-called "fresh-water Radiolaria," which have been described by Focke, Greeff, Grenacher and others, are all Heliozoa, without either central capsule or calymma.
227. Local distribution.—As regards their local distribution and its boundaries the Radiolaria show in general the same relations as other pelagic animals. Since they are only to a very slight extent, if at all, capable of active horizontal locomotion, the dispersion of the different species from their point of development (or "centre of creation") is dependent upon oceanic currents, the play of winds and waves and all the accidental causes which influence the transport of pelagic animals in general. These passive migrations are here, however, as always, of the greatest significance, and bring about the wide distribution of individual species in a far higher degree than any active wanderings could do. Any one who has ever followed a stream of pelagic animals for hours and seen how millions of creatures closely packed together are in a short time carried along for miles by such a current, will be in no danger of underestimating the enormous importance of marine currents in the passive migration of the fauna of the sea. Such constant currents may, however, be recognised both near the bottom of the sea and at various depths, as well as at the surface, and are therefore of just as much significance for the abyssal and zonarial as for the pelagic Radiolaria. It is easy to explain by this means how it is that so many animals of this class (probably indeed the great majority) have a wide range of distribution. The number of cosmopolitan species which live in the Pacific, Atlantic and Indian Oceans is already relatively large. In each of these three great ocean basins, too, many species show a wide distribution. On the other hand, there are very many species which are hitherto known only from one locality, and probably many small local faunas exist, characterised by the special development of particular groups. The observations which we at present possess are too incomplete, and the rich material of the Challenger is too incompletely worked out, to enable any definite conclusions to be drawn regarding the local distribution of Radiolaria.
The statements made in the systematic portion of this Report regarding the distribution of the Challenger Radiolaria are very incomplete. In most cases only one locality is mentioned, and that is the station (§ 240) in the preparations or bottom deposit from which I first found the species in question. Afterwards I often found the same species again in one or more additional stations (not seldom in numerous preparations both from the Pacific and Atlantic), without the possibility of adding them to the habitat recorded under the description. The necessary accurate determination and identification of the species (measuring the different dimensions, counting the pores, &c.), would have occupied too much time, and the writing of this extensive Report would have lasted not ten but twenty or thirty years.
228. Horizontal Distribution.—From the extensive collections of the Challenger and from the other collections which have furnished a welcome supplement to them, it appears that Radiolaria are distributed throughout all seas without distinction of zones and physical conditions, even though these latter may be the cause of differences in their qualitative and quantitative development. In the case of the Radiolaria as well as of many other classes of animals, the law holds good that the richest development of forms and the greatest number of species occurs between the tropics, whilst the frigid zones (both Arctic and Antarctic) exhibit great masses of individuals, but relatively few genera and species (see note A). In the Challenger collection the greatest abundance of species of Radiolaria is exhibited by those preparations which were collected at low latitudes in the immediate neighbourhood of the equator; this is true both of the Atlantic (Stations 346 to 349) and of the Pacific (Stations 266 to 274); in the former the richest of all is Station 347 (lat. 0° 15′ S.), in the latter Station 271 (lat. 0° 33′ S.) (see note B). From the tropics the abundance of species seems to diminish regularly towards the poles, and more rapidly in the northern than in the southern hemisphere; the latter also appears, considered as a whole, to possess more species than the former. A limit to the life of the Radiolaria towards the poles has not yet been found; the expeditions towards the North Pole (see note C), like those towards the South (see note D), have obtained bottom-deposits and ice enclosures which contained Radiolaria; in some of the most northerly and most southerly positions which were reached the number of Radiolaria enclosed in the ice was relatively great.
A. The greater abundance of Radiolaria in the tropical seas is probably to be explained by the more favourable conditions of existence, and in particular the larger quantity of nutritive material (especially of decayed animals) and not by the higher temperature of the surface, for at depths of from 2000 to 3000 fathoms where the abyssal Radiolaria live, the temperature is but little above the freezing point or even below it (compare the bottom temperatures in the list of Challenger Stations, § 240).
B. Station 271 of the Challenger Expedition, situated almost on the equator in the Mid Pacific (lat. 0° 33′ S.), exceeds all other parts of the earth, hitherto known, in respect of its wealth in Radiolaria, and this is true of the pelagic as well as of the zonarial and abyssal forms. In the Station List the deposit at this point is stated to be "Globigerina ooze"; but after the calcareous matter has been removed by means of acid, the purest Radiolarian ooze remains, rich in varied and remarkable species. More than one hundred new species have been described from this Station alone.
C. Regarding the Arctic Radiolaria compare the contributions of Ehrenberg (L. N. 24, pp. 138, 139, 195) and Brady on the English North Polar Expedition, 1875-76 (Ann. and Mag. Nat. Hist., 1878, vol. i. pp. 425, 437).
D. Regarding the Antarctic Radiolaria, compare § 230, note A, and Ehrenberg, Mikrogeologie (L. N. 6, Taf. xxxv., A.), also L. N. 24, pp. 136-139.
229. Fauna of the Pacific Ocean.—From the splendid discoveries of the Challenger, and the supplementary observations obtained from other sources, the Pacific seems to be the ocean basin which is richest both quantitatively and qualitatively in Radiolarian life, excelling both the Indian and Atlantic Oceans in this respect. It may be assumed with great probability that by far the largest portion of the Pacific has a depth of between 2000 and 3000 fathoms, and that its bottom is covered either with Radiolarian ooze (§ 237) or with a red clay (§ 239), which contains many Spumellaria and Nassellaria, and has probably been derived for a great part from broken down and metamorphosed Radiolarian ooze (see note A). Pure Radiolarian ooze was found by the Challenger eastwards in the Central Pacific (over a wide area between lat. 12° N. and 12° S., Stations 265 to 274), and also westwards in the latitude of the Philippines, twenty degrees to the east of them (between lat. 5° N. and 15° N.). The great abundance of Radiolaria present in the neighbourhood of the Philippines and in the Sunda Sea was already known from other investigations (note B). The red clay also, which covers a great part of the bottom of the North Pacific, and which was obtained of very constant composition by the Challenger between lat. 35° N. and 38° N., from Japan to the meridian of Honolulu (from long. 144° E. to 156° W.), is so pre-eminently rich in Radiolaria that it often approaches in composition the Radiolarian ooze, and has probably been derived from it. The track of the Challenger through the tropical and northern parts of the Pacific describes nearly three sides of a rectangle, which includes about half of the enormous Pacific basin, and from this as well as from other supplementary observations it may with great probability be concluded that by far the largest part of the bed of the Pacific (at least three-fourths) is covered either with Radiolarian ooze or with red clay, which contains a larger or smaller amount of the remains of Radiolaria. With this agrees also the important fact that the numerous preparations of pelagic materials and collections of pelagic animals, which were collected by the Challenger in the Pacific, almost always indicate a corresponding amount of Radiolarian life on the surface. This is true in particular also of the South Pacific, between lat. 33° S. and 40° S. (from long. 133° W. to 73° W., Stations 287 to 301); the surface of this southern region and the different bathymetrical zones were rich in new and peculiar species of Radiolaria.
A. Many specimens of bottom-deposits from the Pacific, which are entered in the Challenger lists either as "red clay" or "Globigerina ooze," contain larger or smaller quantities of Radiolaria, and the number of different species of Spumellaria and Nassellaria which they contain is often so great that the deposit might have been almost as appropriately termed "Radiolarian ooze," e.g., Stations 241 to 245, and 270, 271 (compare §§ 236-239).
B. Pacific Radiolarian ooze was first obtained by Lieutenant Brooke (May 11, 1859) between the Philippines and Marianne Islands, from a depth of 3300 fathoms (lat. 18° 3′ N., long. 129° 11′ E.). Ehrenberg, who first described it, found seventy-nine different species of Polycystina in it, and reported "that their quantity and the number of different forms increased with the depth" (Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, 1860, pp. 466, 588, 766).
230. Fauna of the Indian Ocean.—As regards its Radiolarian fauna the Indian Ocean is the least known of the three great basins. Still the few limited spots, regarding which investigations are forthcoming, indicate a very rich development of Radiolarian life. Probably it approaches more nearly the fauna of the Pacific than that of the Atlantic, both as regards the abundance and the morphological characters of its species. The researches of the Challenger are very limited and incomplete as regards the Indian Ocean, for the expedition only just touched upon this great ocean basin (2000 to 3000 fathoms deep) at its two extremities (westwards at the Cape of Good Hope and eastwards at Tasmania), its course lying for the most part south of lat. 45° S. and extending beyond lat. 65° S. (from Station 149 to 158, south of lat. 50° S.). It is true that this portion of the South Indian Ocean was shown to contain Radiolaria everywhere, but these were more plentiful in individuals than in species. Only from Station 156 to Station 159 (between lat. 62° and 47° S., and long. 95° and 130° E.) was the bottom, which consisted partly of Diatom ooze and partly of Globigerina ooze, richer in species (see note A). The gaps left by the Challenger in the investigation of the Indian Ocean, have, however, been to some extent filled from other sources. As early as 1859 the English "Cyclops" expedition had shown that the bottom of the Indian Ocean to the east of Zanzibar (lat. 9° 37′ S., long. 61° 33′ W.) is covered with pure Radiolarian ooze (see note B). Also since the Tertiary rocks of the Nicobar Islands are for the most part of the same composition, and since a great abundance of Radiolaria has been shown to be present both in the east part of the ocean, between the Cocos Islands and the Sunda Archipelago (see note C), and in the northern part or Arabian Sea between Socotra and Ceylon (see note D); it may be assumed with great probability that the greater part of the basin of the Indian Ocean, like that of the Pacific, is covered either with Radiolarian ooze or with the characteristic red clay. With this agrees the richness of the surface of the Indian Ocean in Radiolaria of the most various groups, which has been more extensively demonstrated.
A. The Radiolarian fauna collected by the Challenger on the voyage from the Cape to Melbourne, shows in part, namely, from Station 156 to Station 158, very peculiar and characteristic composition; in particular, the Diatom ooze of Station 157 passes over in great part into a Radiolarian ooze, mainly composed of Sphærellaria. This is worthy of a more thorough investigation than I was able, owing to lack of material and time, to give it.
B. The remarkably pure Radiolarian ooze of Zanzibar, discovered by Ehrenberg in 1859, was the earliest known recent example of that deposit. It was brought up by Captain Pullen of the English man-of-war "Cyclops," from a depth of 2200 fathoms, between Zanzibar and the Seychelles, and "under a magnifying power of 300 diameters, showed at the first glance a mass of almost pure Polycystina, such as no sample of a deep-sea deposit has hitherto shown. It is very noticeable that in the whole of this mass of living forms, no calcareous shells are to be seen" (Ehrenberg, L. N. 24, pp. 148, 149).
C. For the most important material from the Indian Ocean, I am indebted to Captain Heinrich Rabbe of Bremen, who during many voyages in the Indian Ocean, in his ship "Joseph Haydn," made numerous collections in different localities with the tow-net and the trawl, and admirably preserved the rich collections thus made. The greatest abundance of Radiolaria was found in those obtained to the east of Madagascar, and next in those from the neighbourhood of the Cocos Islands. I take this opportunity of expressing my thanks to Captain Rabbe for the liberality with which he placed all this valuable material at my disposal.
D. On my voyage from Aden to Bombay, and thence to Ceylon (1881), and especially on my return journey from Ceylon, between the Maldive Islands and Socotra (1882), I carried on a number of experiments with a surface net, which yielded a rich fauna of pelagic animals, and among them many new species of Radiolaria, for observation. On several nights when the smooth surface of the Indian Ocean, unrippled by any wind, shone with the most lovely phosphorescent light, I drew up water from the surface with a bucket, and obtained a rich booty. A number of other new species of Radiolaria from very various parts of the Indian Ocean I obtained from the alimentary canal of pelagic animals, such as Medusæ, Salpæ, Crustacea, &c. Although the total number of Radiolaria known to me from the Indian Ocean is much less than from the Atlantic and Pacific, there are several new genera and numerous species among them, which show that a careful study of this fauna will be of wide interest.
231. Fauna of the Atlantic Ocean.—The Atlantic Ocean in all parts, of which the pelagic fauna has been examined, has shown the same constant presence of Radiolaria, and in certain parts of its abyssal deposits a larger or smaller quantity of different types belonging to this class; on the whole, however, its Radiolarian fauna is inferior to that of the Pacific, and probably also to that of the Indian Ocean, both in quantity and quality. Pure Radiolarian ooze, such as is so extensively found on the floor of the Pacific, and in certain places in that of the Indian Ocean, has not yet been found in the Atlantic (see § 237). The red clay, too, of the deep Atlantic does not seem to be so rich in Radiolaria as that of the Pacific; nevertheless, the number of species peculiar to the Atlantic is very large, and at certain points the abundance of species as well as of individuals seems to be scarcely less than in the Pacific. This is especially true of the eastern equatorial zone not far from Sierra Leone, Stations 347 to 352 (see note A); also of the South Atlantic between Buenos Ayres and Tristan da Cunha, Stations 324, 325, 331 to 333 (see note B); and, lastly, in the North Atlantic in the Gulf Stream and near the Canary Islands (see note C). The fauna of the latter agrees for the most part with that of the Mediterranean (see note D). In addition to the material collected by the Challenger, other deep-sea investigations have furnished bottom-deposits from different parts of the ocean, which have proved very rich in Radiolaria (see note E). Furthermore, since the island of Barbados consists for the most part of fossil Radiolarian ooze, it is very probable that at certain parts of the tropical Atlantic true Radiolarian ooze, like that of the Pacific and Indian Oceans, will eventually be found in depths between 2000 and 3000 fathoms, perhaps over a considerable area.
A. The tropical zone of the eastern Atlantic seems to be especially rich in peculiar Radiolaria of different species. This is shown by numerous preparations from the surface, and from various depths (between lat. 3° S. and 11° N., and long. 14° W. to 18° W.), which were made towards the end of the cruise. Unfortunately no bottom-deposits were obtained from the most important stations (except Nos. 346 and 347, depths 2350 and 2250 fathoms) in this region; at these the deposit was a Globigerina ooze containing numerous different species of Radiolaria.
B. In the South Atlantic, between Buenos Ayres and Tristan da Cunha (between lat. 35° S. and 43° S., long. 8° W. and 57° W.) there appears to be a long stretch covered partly with Globigerina ooze (Stations 331 to 334), or red clay (Stations 329, 330), partly with blue mud (Stations 318 to 328), which contains not only large masses of individuals but numerous peculiar species of Spumellaria and Nassellaria. The preparations from the surface-takings of this region are also rich in these, as well as in peculiar Phæodaria.
C. The northern part of the Atlantic appears on the whole to be inferior to the tropical and southern portions as regards its richness in Radiolaria, and from the western half more especially, only few species are known. From my researches at Lanzerote in 1866-67, it appears that the pelagic fauna of the Canary Islands is very rich in them, as is also the Gulf Stream in the neighbourhood of the Færöe Channel, according to the investigations of John Murray (see his Report on the "Knight-Errant" Expedition, Proc. Roy. Soc. Edin., vol. xi., 1882).
D. The Radiolaria of the Mediterranean are of special interest, because almost all our knowledge of these organisms in the living conditions and of their vital functions has been derived from investigations conducted on its shores. Johannes Müller laid the foundation of this knowledge by his investigations at Messina, and on the Ligurian and French coasts at Nice, Cette, and St. Tropez (L. N. 10). The many new Radiolaria which I described in my Monograph (L. N. 16, 1862), were for the most part taken at Messina, the place which possesses a richer pelagic fauna than any other, so far as is yet known, in the Mediterranean. Other new species I found afterwards at Villafranca near Nice, in 1864 (L. N. 19), at Portofino near Genoa (1880), at Corfu (1877), and at other points on the coast. In Messina also, Richard Hertwig collected the material for his valuable treatise on the Organisation of the Radiolaria (L. N. 33), after he had previously made investigations into their histology at Ajaccio in Corsica (L. N. 26). Lastly, at Naples, Cienkowski (L. N. 22) and Karl Brandt (L. N. 38, 39, 52) carried out their important investigations into the reproduction and symbiosis of the Radiolaria. With respect to the character of its Radiolaria, the Mediterranean fauna is to be regarded as a special province of the North Atlantic.
E. Among the smaller contributions which have been made towards our knowledge of the Atlantic Radiolarian fauna, the communications of Ehrenberg on the deposits obtained in sounding for the Atlantic cable, and on the Mexican Gulf Stream near Florida, deserve special mention (L. N. 24, pp. 138, 139-145).
232. Vertical Distribution.—The most important general result of the discoveries of the Challenger, as regards the vertical or bathymetrical distribution of the Radiolaria, is the interesting fact that numerous species of this class are found living at the most various depths of the sea, and that certain species are limited to particular bathymetrical zones, i.e., are adapted to the conditions which obtain there. In this respect three different Radiolarian faunas may be distinguished, which may be shortly termed "pelagic," "zonarial," and "abyssal." The pelagic Radiolaria swim at the surface, and when they sink (e.g., in a stormy sea), only descend to a small depth, probably not more than from 20 to 30 fathoms (§ 233). The complicated conditions of existence created by the keen struggle for existence at the surface of the sea, give rise to the formation of very numerous pelagic species, especially of Porulosa (Spumellaria and Acantharia). The abyssal Radiolaria are very different from those just mentioned; they live at the bottom of the deep-sea, not resting upon nor attached to it, but probably floating at a little distance above it, and are adapted to the conditions of existence which obtain there (§ 235). Here the Osculosa (Nassellaria and Phæodaria) seem to predominate. The zonarial Radiolaria live floating at various depths between the pelagic and abyssal species (§ 234). In their morphological characters they gradually approach the pelagic forms upwards and the abyssal downwards.
The views which have hitherto been held regarding the bathymetrical or vertical distribution of the Radiolaria have been entirely altered by the magnificent discoveries of the Challenger, and especially by the important observations of Sir Wyville Thomson (L. N. 31) and John Murray (L. N. 27). These two distinguished deep-sea explorers have, as a result of their wide experience, been convinced that Radiolaria exist at all depths of the ocean, and that there are large numbers of true deep-sea species which are never found at the surface of the sea nor at slight depths (L. N. 31, vol. i. pp. 236-238; L. N. 27, pp. 523, 525). The result of my ten years' work upon the Challenger Radiolaria, and the comparative study of more than a thousand mountings from all depths, has only been to confirm this opinion, and I am further persuaded that it will some day be possible by the aid of suitable nets (not yet invented) to distinguish different faunistic zones in the various depths of the sea. In this connection may be mentioned the specially interesting fact that the species of Radiolaria of one and the same family present in the different depths characteristic morphological distinctions, which obviously correspond to their different physiological relations in the struggle for existence. Owing to those extensive discoveries, the representation which I gave in my Monograph (1862, L. N. 16, pp. 172-196) of the vertical distribution of the Radiolaria, and of their life in the greatest depths of the sea, has been entirely changed. Compare also Bütschli (L. N. 41, p. 466).