428 



NATURE 



[August 28, 1884 



then opened, lowered for some distance, and again closed before 

 it is drawn to the surface. The greatest uncertainty and differ- 

 ence of opinion exist as to whether the intermediate waters are 

 inhabited at all by animals, and, if they are inhabited, to what 

 extent ; and these intermediate waters constitute by far the 

 greatest part of the ocean. If we estimate roughly the depth of 

 the surface-zone inhabited by an abundant pelagic fauna at 100 

 fathoms, and that of the zone inhabited by the bottom animals 

 at 100 fathoms also, the average depth of the ocean being about 

 1S80 fathoms, it results that the intermediate waters, concerning 

 the conditions of life in which we are at present in the utmost 

 uncertainty, really represent more than eight-ninths of the bulk 

 of the entire ocean. Great care should be exercised in drawing 

 conclusions from the depths ascribed to animals in some of the 

 memoirs in the official work on the Challenger Expedition. The 

 scientific staff of the Expedition merely recorded on each bottle 

 containing a specimen the depth from which the net in which the 

 .specimen was found had been drawn up. In many instances, 

 from the nature of the specimen, it is impossible that it can have 

 come from anywhere but the bottom, but in many others it is 

 quite possible that a particular specimen may have entered the 

 net at any intermediate depth, or close to the surface, and this 

 is a matter on which the author of the monograph in which the 

 specimen is described can form the best conclusion, if one can be 

 formed at all from his knowledge of the animal itself. In all 

 doubtful cases the mere record of the depth must be received 

 with caution. 



Just as before the commencement of the present period of 

 deep-sea research there was a strong tendency amongst naturalists, 

 owing to the influence of the views of Edward Forbes, to refuse 

 to accept the clearest evidences of the existence of starfish and 

 other animal life on the sea-bottom at great depths, so there 

 seems now to have sprung up in certain quarters an opposite 

 tendency, leading to the assignment of animals possibly of surface 

 origin to great depths on inconclusive evidence. 



With regard to the constitution of the deep-sea fauna, one of 

 its most remarkable features is the general absence from it of 

 Palaeozoic forms, excepting so far as representatives of the 

 Mollusca and Brachiopoda are concerned, and it is remarkable 

 that amongst the deep-sea Mollusca no representatives of the 

 IVaulilidtz and AmmoniliJce, so excessively abundant in ancient 

 periods, occur, and that Llngu/a, the most ancient Brachiopod, 

 should occur in shallow water only. 



There are no representatives of the most characteristic of the 

 Palaeozoic coraLs, such as Zaphrentis, Cystiphyllum, Stauria, or 

 Goniophyllum. Possible representatives of the Cyathonanida 

 have indeed been obtained in Gruyina, described by Prof. 

 Martin Duncan, and Haplophyllia and Duncania, described by 

 the late Count Pourtales, but the Cyathonanldie are the least 

 observant and characteristic members of so-called Rugosa. 

 Pourtales justly felt doubtful whether the arrangement of the 

 septa in four systems instead of six could in itself be considered 

 as a criterion of the Rugosa, 1 and in the cases of Haplophyllia and 

 Duncania the septa may be described rather as devoid of any 

 definite numerical arrangement than exhibiting any tetrameral 

 grouping. Further, I have lately examined by means of sections 

 the structure of the soft parts of Duncania in a specimen kindly 

 given to me by Mr. Alexander Agassiz for the purpose, and find 

 that with regard to the peculiar arrangement of the longitudinal 

 septal muscles and the demarcation of the directive septa the 

 coral agrees essentially with the henactinian Caryophyllla and 

 all other modern Madreporaria the anatomy of which has been 

 adequately investigated. 



There are further no representatives of the ancient Alcyo- 

 narlans, forming massive coralla, the Helioporida and their 

 allies, in deep water, no Paheocrinoids, Cystidea, or Blastoldea, 

 no Palechinoidea, no Trilobltes, no allies of Limulus, no Ganoids. 

 Further, other ancestral forms, certainly of great antiquity, 

 although unrecorded geologically, such as Amphioxus, do not 

 occur in deep water. It might well have been expected that, 

 had the deep sea been fully colonised in the Palaeozoic period, 

 a considerable series of representative forms of that age might 

 have survived there in the absence of most of the active physical 

 agents of modification which characterise the coast regions. 



From the results of present deep-sea research, it appears that 

 almost all modern littoral forms are capable of adapting them- 

 selves to the conditions of deep-sea life, and there is no reason 

 why Palaeozoic forms should not have done so if the abyssal 



1 "Zoological Results of the Hassler Expedition." See Cat. Mus. Co/tip. 



■ viii. r?7.|, p 14. 



conditions were similar to those now existing, just as a con- 

 siderable number of forms of the chalk period have survived 

 there. In fact, however, most of the survivals of very ancient 

 forms — Hellopora, Limulus, Amphioxus, Dipnoi, Ganoids — 

 occur in shallow seas or fresh water. 



With regard to the origin of the deep-sea fauna, there can be 

 little doubt that it has been derived almost entirely from the 

 littoral fauna, which also must have preceded, and possibly given 

 rise to, the entire terrestrial fauna. Although the littoral, and 

 even its offspring, the terrestrial faunas, have undoubtedly, 

 during the progress of time, contributed to the pelagic fauna, 

 and although it is very likely that the first traces of life may have 

 come into existence in the shallow waters of the coast, it is not 

 improbable that we should look to the pelagic conditions of 

 existence as those under which most of the earliest types of 

 animal life were developed. Nearly all the present inhabitants 

 of the littoral zone revert to the pelagic free-swimming form of 

 existence in their early developmental stages, or in cases where 

 these stages have been lost can be shown to have once possessed 

 it. And these pelagic larval forms are in many cases so closely 

 alike in essential structure, though springing from parents allied 

 but widely differentiated from one another in the adult form, 

 that it is impossible to regard them as otherwise than ancestral. 

 Had they been produced by independent modification of the 

 early stages of the several adult forms as a means of aiding in 

 the diffusion of the species, they must have become more widely 

 differentiated from one another. The various early pelagic free- 

 swimming forms, represented now mostly only by larvae, gradually 

 adapted themselves to coast life, and underwent various modifi- 

 cations to enable them to withstand the beating of the surf on 

 tlie shores and the actual modifying alterations of the tides, 

 which, together with other circumstances of coast life, acted as 

 strong impulses to their further development and differentiation. 

 Some developed hard shells and skeletons as protections ; others 

 secured their position by boring in the rocks or mud ; others 

 assumed an attached condition, and thus resisted the wash of 

 the waves. A remarkable instance in point, about the circum- 

 stances of which there can be little doubt, is that of the Cirripedia. 

 The Cyprls larva of Balanus, evidently of pelagic origin, sprung 

 from a Naupllus, fixes itself by its head to the rocks and 

 develops a hard conical shell, by means of which it withstands 

 the surf in places where nothing else can live. In the same way 

 the Planula larva, the Palaeozoic ccelenterate form, produces the 

 reef coral and various other forms specially modified for and by 

 the conditions of littoral existence. Similarly echinoderms, 

 Mollusca, Polyzoa, Crustacea, recapitulate in their ontogeny their 

 passage from a pelagic into a littoral form of existence. 



It is because the ancestors of nearly all animals have passed 

 through a littoral phase of existence, preceded mostly by a pelagic 

 phase, that the investigations now being carried on on the coasts 

 in marine laboratories throw floods of light on all the fundamental 

 problems of zoology. From the littoral fauna a gradual mign tion 

 must have taken place into the deep sea, but probably this did 

 not occur till the littoral fauna was very fully established and 

 considerable pressure was brought to bear on it by the struggle 

 for existence. Further, since a large share of the present food 

 of deep-sea animals is derived from coast-debris, life must have 

 become abundant in the littoral zone before there could have 

 been a sufficient food-supply in the deeper regions adjoining it. 

 Not until the development of terrestrial vegetation and animal 

 life can the supply have reached its present abundance. Such a 

 condition was, however, certainly reached in the Carboniferous 

 period. From what has been stated as to the general absence 

 of representatives of Palaeozoic forms from the deep sea, it is 

 just possible that if deep oceans existed in Palaeozoic periods 

 they may not have been colonised at all, or to a very small 

 extent, then, and that active migration into deep waters com- 

 menced in the secondary period. Very possibly the discharges 

 of carbonic acid from the interior of the earth, which Prof. 

 Dittmar believes may have been sufficient to account for the vast 

 existing deposits of coal and limestone, may have been much 

 more abundant than at present over the deep-sea beds in the 

 Palaeozoic period, and have rendered the deep waters more or 

 less uninhabitable. 



In his splendid monograph on the Pourtalcsla, x which has 

 recently appeared, Prof. Loven has dwelt on the peculiar 

 importance of the littoral region, and of the infinity of agencies 

 present in it " competent to call into play the tendencies to vary 



■ On Pourtalcsia, a Croup of Echinoidca, by Even Loven. (Stockholm. 

 1883.) 



