ON CRUSTACEA. 
253 
state of exhaustion which lasts many days, until the most ex- 
ternal part of the dermis is filled with calcareous molecules, 
which re-establish its solidity. 
In the entomostraca, whose growth is much more rapid than 
that of the Crustacea properly so called, and in which the 
duration of life is extremely short, the moultings succeed each 
other quickly. Thus, M. de J urine, who observed the daphnia 
from the moment of their birth to that of their first ovideposi- 
tion, counted, in an interval of seventeen days, eight moultings, 
which took place pretty nearly within two days’ interval of 
each other. lie did not pursue his observations on those 
changes of skin beyond this point, as they succeed each other 
in the same manner in summer up to, the death of the animal. 
In winter the moultings are very much retarded, and it is not 
uncommon for eight or ten days to elapse between them. 
In cypris, apus, branchipus, lynceus, limnadia, and poly- 
phemus, the moultings are also very frequent. 
In all the Crustacea and entomostraca, it is remarked that 
the old skin is composed of all the principal or accessory parts 
which belong to the animal, and that often each spine or each 
hair there is hollow, and covers another spine or another hair. 
The chemical analysis of the old testa demonstrates that it is 
formed of carbonate and phosphate of lime, united to gelatine 
in various proportions, which are generally in relation to the 
solidity of the testa. 
We proceed to a few observations on the function of Nu- 
trition in the Crustacea. Most of these animals feed upon 
solid substances, and generally on animal matters more or 
less in a state of decomposition. There are, however, some 
among them that live on fluids, which they suck from the ani- 
mals to which they are parasitically attached. 
The former are all provided with a mouth more or less com- 
plicated, and composite, as we have already seen, and fur- 
nished with a variable number of organs for mastication or 
