148 PRIMITIVE FORMS OF LIFE 



This fauna is completed by the turtles and the Cetaceans, 

 representing a special adaptation of Mammals to marine life. 

 It is obviously quite fragmentary, and the presence of turtles 

 and Cetaceans indicates an immigration from the coasts. 



The fauna of the ocean depths is no less incomplete. 1 

 When it was discovered, an idea became prevalent that 

 the depths of the ocean were particularly rich. Having 

 had the opportunity of studying the excellent collections of 

 Starfish gathered by Alexander Agassiz in the Caribbean Sea, 

 and those obtained in the Atlantic by the Travailleur and 

 Talisman expeditions, I had the curiosity to investigate how 

 often the dredge would have to be let down to bring up a single 

 organism of any kind, a species, or a genus, according as the 

 depth increased. The figures mounted progressively for the 

 three cases, which implies that the fauna of the depths 

 diminishes and becomes impoverished as regards the number of 

 species and genera as we go deeper.' It is therefore evident that 

 the depths of the sea are not, as was once believed, a reserve 

 of living forms. On the contrary, life reaches these depths 

 very slowly, and comes not from the surface, which, as we have 

 seen, was peopled in a special way and possesses only a 

 fragmentary fauna, but from the shore. In fact, all the species 

 of Starfish found at great depths are represented along the 

 shores by analogous species ; but the littoral species, which 

 can be regarded as the forbears of the deep sea species, are 

 scattered along the coasts in such a way that all the coasts may 

 claim to have supplied their contingent to the deep sea fauna. 



These considerations almost dispense with the necessity of 

 having to examine the nature of this fauna in order to establish 

 its littoral origin. But it will furnish valuable evidence in 

 support of our point of view. We must make an important 

 preliminary distinction at the outset. Down to a depth of 

 fifteen hundred to two thousand metres we do find an increase 

 in species belonging to groups that flourished during the 

 Secondary Period and have since then become rarer or have 

 even completely disappeared along the coasts. Such, for 

 instance, among the "Phytozoa", are the glassy Hexact- 

 inellid Sponges, the hydrocoralines, the solitary corals 



1 LIV, 336. 



