752 report — 1884. 



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 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 deve- 

 loped. 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 lame, gradually 

 adapted themselves to coast life, and underwent various modifications to enable 

 them to withstand the beating- of the surf on the 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 circumstances 

 of which there can be little doubt, is that of the Cirripedia. The cypris larva of 

 Balanus, evidently of pelagic origin, sprung from a Nauplius, fixes itself by its 

 head to the rocks and develops a hard conical shell, by means of which it withstand^ 

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

 larva, the Palaeozoic coelenterate 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 

 migration 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 vege- 

 tation 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 commenced in the secondary period. Very possibly the 

 discharges of carbonic acid from the interior of the earth, which Professor 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 Pourtalesia, 1 which has recently appeared, 

 Professor 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 which are embodied in each species.' He treats of the origin of 

 the deep-sea fauna from that of the littoral region. It is impossible here to follow 



1 On Pourtalesia, a Group of Ecldnoidea, by Sven Loven. Stockholm, 1 883. 



