48 



Jud^i'cd iron the standpoints of individual abundance and of ;.bil- 

 itv to ,.,coplG all :..nrts of tha sea, marine marnn^als have not been go 

 succes,3ful^•^3 the fishes. On land, on the other hand, the wam- 

 blooded ma.:L:ials a:id birds have, in the lor'j; run, proven rr.ore r5uc- 

 cessful than the cold-blooded reptiles or araphibians up to daio. 



These t::ierrnal differences between the aquatic and terrestric-1 

 enviroa::ient i:xke it far simpler to study tne relationchips tha.-": the 

 activicies of the organism as a ^.^hole (as distinguished from its 

 several constituent tissues) bear to te:r.perature aiaong m-nrine ■jx 

 fresh--;/atcr, than anong land ani.aals. And the control that te.-iv'-r- 

 ature exerts en the life processes i.^a'ces this a very important 

 question in relation to aniaial economy in general, 



Tae aquatic environner^t, by its comp-rative opacity to sol:'r 

 radiation also protects all of its inhabitants, er.cept such ai live 

 close to th'i surface, from the effects of sunlight. This fre-s the 

 organisn from the need of developing any opaque covering to prot ..-ct 

 it for, essential though the sunlight be in vital economy, the 

 shorter v;avc lengths are deadly to protoplasm. There is no dan;:cr 

 in the rea of the sunburn against which every terrestrial ani no.l 

 must in so/ne way protect i'.-s tissues. One of the chief factors that 

 controls the development of pigmentation among land animals thus 

 plays 1 ::.uc:i less im;ortant role in the sea, allowing pigment ..luch 

 ]:!ore di:^'^ctly to reflect the internal metabolic activities. Ooranct- 

 ed with t-is is the very interest '.ng general rule that, wher.a"! on 

 land animals living in dn,rknesn are usually colorless, in the ocean- 

 abyss below the influence of the sun's rays they are as a rule in- 

 tensely^ pig-''}.ented, and often velvety blach. This difference reflects 

 in th.=^ one cn-se the loss of pigm.ent previously developed by th'' c'.n- 

 cestral forms that lived in sunlight, but in the other case the dcv- 

 elopm.ent of pigment untrammolcd by light, its causes as yet unl:no\7n. 



Because of the r-ipid gradation in the strength of light fr' ;.• 

 the surfcacc of the sea dornv/ard, and be&asue of the ability of :.:■- 

 imals to escape light by sinking, the sea offers a far better opyort- 

 unity than dors the land to study the whole category of tropisms 

 that light stimulation ca.uses; also the natural economy of ani.xls 

 that live perLa,ncntly in total darkness, as well as the whole cor- 

 plex of oroblcms that center about animal lixnineseence. 



The high specific gravity of s -^a water, the fact that it is an 

 aqueous solution, its Gom.p.':.ratively constant temperature, th.) pro- 

 tection that a very thin film, of it gives against sunlight, and its 

 inces-.ant motion, make:, the whole problem of rcprodiicti n much s'm- 

 pler for mjarinc than for terrestrial animals. Eggs need less pro- 

 tection, and the young hatched therefrom, are capable of independent 

 existence at tt. earlier stage in development thian is the rule -in 

 land. £o w; find that even the most highly organized of the aaimels 

 of direct marine ancestr^r (the bony fishes) as a group solve the re- 

 producbivo orcblem mer ly by producing a grc'^-t many eggs, witiiov.t 

 any co.uplox arrangements for nursing the latter, or caring for the 

 young, while larvae developm.ent is m.uch more usual in the sea than 

 on lanl. It is true that so 'e fishes (notably the shark",) ar : vivi- 

 parous, but j edged by the usual criteria this does not so;.m; t :> have 

 been of any great advantage in group evolution in the soa. 



