152 Pelagian Mollusca collected on a [no. 2, new series* 



in their earlier stages of existence. I have watched the young of 

 several species of Cyprcea when first disengaged from the egg or 

 nidamental capsule. The foot of the animal then unadapted for 

 crawling is expanded into two slender fins by means of which these 

 little creatures swim with rapid jerking movements and having 

 little or no voluntary power of directing these motions, they are 

 carried by a blind instinct or rather in obedience to the laws of 

 the great author of nature, wherever they can insure safety from 

 enemies and a sufficiency of their proper sustenance. 



I have been much struck with the resemblance the Pteropod 

 bears to the rudimentary Gastehopod, in its simple organization 

 and in the random jerking manner in which it effects locomotion, 

 apparently with little or no exercise of volition. Their chief use 

 in the animal economy seems to be, to afford food to the whale 

 and to various oceanic birds, most of which being night feeders, 

 the Pteropods readily become their prey. It has been already 

 observed that Pteropods, with very few exceptions, shun the 

 light. The different species have their regular periods for approach- 

 ing the surface of the water, where they actively sport about for a 

 given time and then retire from view, to be succeeded by other, 

 species which also play their part on the surface and then likewise 

 disappear. The cause or object of these periodical visits is un- 

 known, nor has it been ascertained to what depth they subsequently 

 retire. It may be safely assumed that they never reach the bed of 

 the ocean. In the parts where they chiefly abound, the enormous 

 depth of water would forbid this supposition. Being creatures ex- 

 tremely sensitive to light, it is probable that they merely retire to 

 a depth sufficient to enable them to enjoy the required amount of 

 shade or obscurity, besides which their specific gravity differs so 

 slightly from that cf the surface water, that each species when in 

 a state of repose, would probably retain its proper level without 

 requiring the exertion of any voluntary effort, 



The Hyalceas when placed in a vessel of water, displayed consi- 

 derable activity, especially the more globose species represented in 

 Fig. 13, which darted about in all directions by rapidly flapping its 

 fins, which in shape were not unlike a butterfly's wings. The shell 



