178 THREE CRUISES OF THE “ BLAKE." 
generally pass the day resting upon the bottom, with their ten- 
tacles turned upwards, the dise pulsating slowly while at rest. 
The young are far more active than the adult, which, when thus 
half buried in coral mud, resemble huge actiniz with fringed 
tentacular lobes (Phytactis) fully expanded. 
Fig. 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. 
