184 The Science of Life. 



some of them, such as the whales and a small oceanic 

 insect, Halobates, have returned thence to pelagic life. 



"The deep-sea fauna has probably been formed al- 

 most entirely from the littoral, not in the most remote 

 antiquity, but only after food, derived from the debris 

 of the littoral and the terrestrial faunas and floras, be- 

 came abundant in deep water. 



" It was in the littoral region that all the primary 

 branches of the zoological family tree were formed; all 

 terrestrial and deep-sea forms have passed through a 

 littoral phase, and amongst the representative of the 

 littoral fauna the recapitulative history, in the form of 

 series of larval conditions, is most completely retained." 



(b) According to Professor W. K. Brooks and others, 

 the primitive fauna was pelagic. From this have been 

 derived the tenants of the shore and of the deep sea. 

 To the latter, however, he does not deny the possibility 

 of ascending again. The relative easiness of life in the 

 open sea and the unlimited supply of simple Algae are 

 especially suggestive in connection with this theory. 



(c) According to Professor A. Agassiz, Prof. H. Sim- 

 roth, and others, if we may venture to compress their 

 views into a sentence, a littoral fauna was the original 

 one, whence have been derived, on the one hand, the 

 pelagic and abyssal faunas, and, on the other hand, the 

 fresh- water and terrestrial faunas. 



(d) Sir John Murray has emphasized the importance 

 of the mud-line as, at any rate, important headquarters 

 of animal life, and as the area from which wanderers 

 have sunk down to the great abysses. 



