THE RELATIONS OF THE ABYSMAL ZONE 53 



cetacea, most fishes, and perhaps also many cephalo- 

 pods. This portion of the fauna has been called the 

 Nekton. 



And lastly we have those animals that remain 

 perfectly fixed to the bottom or are capable only 

 of creeping or crawling over the rocks and sand, 

 such as the sponges, hydroids, sedentary tunicates, 

 gasteropods, most lamellibranchs. and many crus- 

 tacea. This portion of the fauna has been called the 

 Benthos. 



Although it will not be necessary to use these 

 terms very frequently in this little book, it may be 

 advisable for the reader to bear in mind that in any 

 exhaustive treatise on the marine fauna such terms 

 would be employed, and that in the chapters dealing 

 with the fauna of the abysmal zone we should find 

 accounts of the ' bathybial plankton,' the ' bathybial 

 nekton,' and the ' bathybial benthos.' 



Lastly we must consider quite briefly the views 

 that have been held concerning the origin of the 

 abysmal fauna. 



As soon as it became clear to naturalists that 

 there is no part of the ocean, however deep it may 

 be, that deserves the name ' azoic,' but that almost 

 every part has a fauna of greater or less density, 



