NA TURE 



\_Nov. 4, 1880 



rate, of the secrets of the busy hfe which, contrary to all 

 the beliefs of the naturalists of a past generation, blindly 

 toils and moils in the darkness and cold of the marine 

 abysses. 



The latter half of the " Introduction " will be no less inter- 

 esting to the biologist, since it embodies the general con- 

 clusions at which the scientific director of the Expedition 

 has arrived, in a dissertation on the natureand distribution 

 of the fauna of the deep sea. 



Sir W. Thomson considers that the most " prominent 

 and remarkable biological result " of the four years' work 

 of the Challenner is the final establishment of the fact 

 "that the distribution of living beings has no depth-limit, 

 but that animals of all the marine invertebrate classes, and 

 probably fishes also, e.xist over the whole of the floor of the 

 ocean." As to the exact nature of this deep-sea fauna at 

 the greatest depths, he speaks with some hesitation ; but, 

 at about 2000 fathoms, the list given on pages 36 and 37 

 proves that there is a large and a varied assemblage of 

 forms of life. Upwards, this cliaracteristic deep-sea 

 fauna extends to about 600 fathoms, and is richest 

 between this depth and 1000 or 1200 fathoms. Around 

 all coasts, in temperate regions, the local shore forms, 

 which occupy successive zones of depth as, on land, 

 they characterise zones of height, gradually die out 

 towards the 200-fathom line. Nor is there any close 

 relation between the abyssal and the shore faunx of any 

 given latitude or longitude — on the contrary, the abyssal 

 fauna is singularly uniform and appears "to have been 

 derived from a genetic source different from that of the 

 shore fauna." In fact. Sir Wyville Thomson appositely 

 compares the abyssal ocean — that is the sea everywhere 

 below 200 fathoms or thereabouts — to a world-wide lake 

 of comparatively still water, which, in its deeper parts, is 

 very cold, its temperature neither rising nor falling appre- 

 ciably beyond the average of 35° F. 



Thus there is a certain parallel between land and sea 

 distribution, inasmuch as all Alpine florae present marked 

 analogies with circumpolar florae. The cold land is discon- 

 tinuous, whence it presents, as it were, islands of analogous 

 population all over the world ; while the cold water being 

 continuous, the continuity in its population is correspond- 

 ingly unbroken. But the uniformity and invariability of 

 conditions is far more complete in the abyssal lake than 

 on the mountain-tops ; and the homogeneity of the popu- 

 lation harmonises with that of the medium in whicli it 

 lives. 



Sir Wyville Thomson draws attention to the fact that 

 this widespread abyssal fauna 



" . . . . has a relation to the deep-water fauna of tlie 

 Oolite, the Chalk, and the Tertiary formations, so close 

 that it is difficult to suppose it in the main other than the 

 same fauna which has been subjected to a slow and con- 

 tinuous change under slightly varying circumstances 

 according to some law, of the nature of which we have 

 not as yet the remotest knowledge" (p. 49). 



" There is every reason to believe that the existing 

 physical conditions of this area date from a very remote 

 period, and that the present fauna of the deep sea may 

 be regarded as directly descended from faunje which have 

 necessarily occupied the same deep set. . . . That the 

 present abyssal fauna is the result of progressive change 

 there can be no room for doubt ; but it would seem that 

 in this case, the progress has been extremely slow, and 

 that it has been brought about almost in the absence of 



those causes — such as minor and local oscillations of the 

 crust of the earth producing barriers and affecting climate — 

 on which we are most inclined to depend for the modifi- 

 cation of faunre. The discovery of the abyssal fauna, 

 accordingly, seems to have given us an opportunity of 

 studying a fauna of extreme antiquity, which has arrived 

 at its present condition by a slow process of evolu- 

 tion from which all causes of rapid change have been 

 eliminated" (p. 50). 



That the deep-sea fauna presents us with many forms 

 which are the dried and but little modified descendants 

 of Tertiary and Mesozoic species is a proposition which 

 few who attend to the evidence will be disposed to deny. 

 But I may venture to express some doubt, whether it 

 may not be well to keep a conclusion of such gravity 

 and so well founded, apart from views respecting the 

 absence of "minor local oscillations of the crust of the 

 earth " in the area of the present great ocean basins, 

 which Sir Wyville Thomson expresses more fully else- 

 where. 



" There seems to be sufficient evidence that all changes 

 of level since the close of the Paleozoic period are in direct 

 relation to the present coast lines. 



" There does not seem to be a shadow of reason for 

 supposing that the gently undulating plains, extending for 

 over a hundred million of square miles, at a depth of 

 2500 fathoms beneath the surface of the sea, and pre- 

 senting, like the land, their local areas of secular eleva- 

 tion and depression, and their centres of more active 

 volcanic disturbance were ever raised, at all events in 

 mass, above the level of the sea ; such an arrangement, 

 indeed, is inconceivable" (p. 46). 



I must plead ignorance of the " sufficient evidence " to 

 which Sir Wyville Thomson refers ; in fact, I should have 

 thought that the sufficient evidence lay in the other 

 direction. Surely there is evidence enough and to spare 

 that the Cretaceous sea, inhabited by various forms, some 

 of whose descendants Sir W. Thomson, as I believe 

 justly, recognises in the present deep-sea fauna, once 

 extended from Britain over the greater part of Central and 

 Southern Europe, North Africa, and Western Asia to the 

 Himalayas. In what possible sense can the change of 

 level which has made dry land and sometimes mountain 

 masses of nine-tenths of this vast area be said to be 

 "in direct relation to the present existing coast lines"? 



That the abyssal plains were ever all elevated, at once, 

 is certainly so improbable that it may justly be termed 

 inconceivable ; but there is nothing, so far as I am aware, 

 in the biological or geological evidence at present ac- 

 cessible, to render untenable the hypothesis that an 

 area of the mid-Atlantic or of the Pacific sea-bed as big 

 as Europe should have been upheaved as high as Mont 

 Blanc and have subsided again any time since the 

 Pateozoic epoch, if there were any grounds for enter- 

 taining it. 



In concluding the " Introduction" Sir Wyville Thomson 

 expresses "a strong personal impression " on two points. 

 The one is that the study of the abyssal fauna lends a 

 powerful support to the doctrine of evolution. The other 

 is, that " the character of the abyssal fauna refuses to give 

 the least support to the theory which refers the evolution 

 of species to extreme variation guided only by natural 

 selection." But the grounds assigned for the latter opinion 

 are hardly so cogent as might be desirable. 



" Species are just as distinctly marked in the abyssal 



