752 



REPORT — 1884. 



preceded, and possibly given rise to, tlie entire terrestrial fauna. Altboue-h the 

 littoral, and even its offsprinji:, the terrestrial faunas, have undoubtedly, duriiifr the 

 progress of time, contributed to the pelagic fauna, and although it is very likeiv 

 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 wen- deve- 

 loped. Nearly all tiie present inhabitants of the littoral zone revert to the pelagic free- 

 .swimming form of existence in their early devflopuiental stages, or in cases where 

 these stages have been lost can be shown to have once possessed it. And tiie.«e 

 pelagic larval forms are in many cases so closely alike in essential structure, 

 though springing from parents allied but widely ditl'erentiated from one another 

 in the adult form, that it is impossible to regard them as otherwise than aiifestrnl, 

 Had they been produced by independent modification of tlie early stages of the 

 several adult forms as a means of aiding in the dili'usion of the species, they mm 

 have become more widely dill'erentiated from one another. The various early 

 ])elagic free-swimming forms, represented now mostly only by larv.T, gradually 

 adapted themselves to coast life, and underwent varioi..< modifications to enable 

 them to with.stand the beating of the surf on the shores and the actual modifviiiir 

 alterations of the tides, which, together with otlier circumstances of coa.vt life, 

 acted as strong impulses to their further development and diilerentiation. 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 resi.sfed 

 the wash of the waves. A remarkable instance in point, about the circumstances 

 of which there can be little doubt, is that of the Cirrippclta. The n/pris larva nf 

 Balfi)m>\ evidently of ])elagic origin, sprung from a Xaup/iiis, 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 Plamh 

 larva, the Palajozoic 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 

 migration must have taken place into the deep sea, but probably this did not occur 

 till the littoral fauna was vt-ry 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 vpge- 

 tation and animal life can the supply have reached its present abundance. Sucli 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 PaliEOzoic 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 Palteozoic period, aud have rendered the aeep waters more or less 

 uninhabitable. 



In his splendid monograph on the rourtalesia,^ 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 .opecies.' He treats of the origin of 

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



' On, Povrtalesia, a Group of Echinmdea, by Sven Loven. Stockholm, 1883. 



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