38 LIVERPOOL MARINE BIOLOGY COMMITTEE REPORT. 



of animals as due to a tendency to recapitulate in their 

 individual development the characters of their ancestors. 



Turning now to the relations of the shallow water fauna 

 to the other faunas, we find that, though animal life is 

 present on the bottom of the ocean at all depths, yet that it 

 is not nearly so abundant at extreme as at moderate depths. 



Concerning the deep-sea animals, we find the fauna is a 

 very miscellaneous collection, including representatives of all 

 the main groups of animals. We find further, that although 

 some of the deep sea forms, notably the curious group of 

 Holothurians known as Elasipoda, are more primitive than 

 their shallow water allies, yet that this is not true of the deep 

 sea fauna as a whole. Indeed, of the more archaic or primi- 

 tive forms in existence at the present day, some, as Limulus, 

 Amphioxus, the Ganoids, and the Dipnoi, are either shallow 

 water or fresh water forms ; while those that do occur in 

 deep water, such as Pentacrinoids and Brachiopoda, are found 

 in shallow water as well. 



The general conclusion, then, to which we are led is that 

 the deep sea fauna is not, as was once supposed, an essen- 

 tially primitive one ; that there is no evidence of the shallow 

 water fauna having been derived from it ; but that, on the 

 other hand, the actual facts are much better explained by 

 supposing the deep sea fauna to consist of forms that have 

 been driven down from shallow water, by the struggle for 

 existence, to regions where opportunities for bettering them- 

 selves are indeed not so great, but where competition is less 

 keen. 



A final argument may be derived from the supply of food. 

 The deep sea has no ultimate supply of food in itself, for, as 

 we have seen, plant life is unknown in it. Hence it is 

 impossible that a deep sea fauna should have existed before 

 a pelagic, or else a shallow water, fauna and flora had become 

 well established. 



