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 Pteeopod 
bears to the rudimentary Gjlsteropod, in its simple organization 
and in the random jerking manner in which it efl"ects locomotion, 
apparently with little or no exercise of volition. Their chief use 
in the animal economy seems to be, to afi'ord food to the whale 
and to various oceanic birds, most of which being night feeders, 
the PTEEOPODS readily become their prey. It has been already 
observed that Pteeopods, 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, ncr has it been ascertained to what depth they subsequently 
retire. It may be safely assumed that they never reach the bed of 
the ccean. 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 HyalcBas when placed in a vessel of water, displayed consi- 
derable activity, especially the more globose species represented in 
Fig. 13, v\hich darted about in all directions by rapidly flapping its 
fins, which in shape were not unlike a butterfly's wings. The shell 
