178 



THREE CRUISES OF THE " BLAKE 



generally pass the day resting upon the bottom, with their ten- 

 tacles turned upwards, the disc pulsating slowly while at rest. 

 The young are far more active than the adult, which, when thus 

 half buried in coral mud, resemble huge actiniae with fringed 

 tentacular lobes (Phytactis) fully expanded. 





83. — Polyclonia frondosa. -j. (Agassiz.) 



How far down the pelagic fauna sinks during the day or night 

 to get out of reach of disturbances is not yet accurately known; 

 we can only form a rough guess from the few experiments made 

 on the " Blake," to be found farther on. The lowest point is 

 probably not far from one hundred and fifty fathoms, which is 



Fig. 84. — Copepod. Greatly magnified. 



perhaps the limit also of the greater superficial disturbances of 

 heat, light, and motion within which we may imagine the pela- 

 gic fauna to oscillate. 



