ON GASTEROPODA. 349 
small masses, glairy, translucent, and ovaliform, composed 
of a greater or less quantity of eggs. These eggs, at first, by 
no means distinct, become so by degrees. In each of them 
the little animal provided with its shell, is very distinguish- 
able, and in a little time it separates from the others and 
proceeds in search of its food. 
We are ignorant of the duration of the life of these animals, 
and of the time which they take to become adult. In certain 
localities they are accumulated in great abundance. 
The limnee are of no direct utility to the human species. 
They serve as food to aquatic birds, and particularly to fishes, 
which consume great quantities of them. 
The species of this genus appear, along with the physe, 
planorbes, &c. to be found in the fresh waters of all parts of 
the earth. ‘They are known in the Northern Zone, in Europe, 
in Asia, and in America. ‘The temperate zone assuredly con- 
tains them in the three quarters of the world. They are found 
in the tropical regions of America, Africa, and Asia. Finally, 
if we are not acquainted with them in the antarctic, or 
southern zone, it is probably owing to the want of direct 
observations. 
We have nothing to add on the rest of this order. 
The second order of this class is the NUDIBRANCHIA. In 
this DoRIs constitutes a very numerous genus. Bohadsch 
first established this genus under the name of Argo, derived 
from this curious reason, that he thought the upper tentacula 
of many species, which are formed as it were of an aggrega- 
tion of small rounded tubercles, were an agglomeration of 
eyes. ‘The details of the organization are curious, but our 
limits oblige us to omit them, and rest contented with the 
brief description in the text. 
The Dorides are hermaphrodites, the two sexes being united 
in each individual. The dorides are all marine, and live at 
variable depths, in rocky situations, where alge, and marine 
