CHAPTER VI 



THE VERMES AND MOLLUSCA OF THE DEEP SEA 



It has not been my intention in tliis volume to con- 

 fine my attention to the truly abysmal forms, but 

 rather to consider all those animals living in deep 

 water that show any characters strikingly different 

 from their relatives living in shallow water. 



The term deep water is, after all, only a relative 

 one. 



To one accustomed only to shore collecting, ten 

 fathoms is deep water, while on the other hand, to 

 such naturalists as those on board the ' Challenger,' 

 who are accustomed to dredge in all seas, nothing 

 under 1,000 fathoms is considered deep water. 



We must bear in mind, however, that at a depth 

 of only 200 fathoms, the conditions of life are very 

 different to those of the shore waters. We find a 

 very great diminution in the amount of light, for In- 

 stance, that can penetrate through sea water teeming 



