CRUSTACEA. 
151 
CLASS f. 
CRUSTACEA. 
The Crustacea are articulated animals, with arilculated feet, re- 
spiring by means of branchiae, protected in some by the borders of 
a shell, and external in others, but which are not inclosed in special 
cavities of the body, and Avhich receive air from openings in the sur- 
face of the skin. Their circulation is double, and analogous to that 
of the Mollusca. The blood is transmitted from the heart, which is 
placed on the back, to the different parts of the body, whence it is 
sent to the branchiae, and thence back again to the heart *. These 
branchiae, sometimes situated at the base of the feet, or even on 
them, at others on the inferior appendages of the abdomen, either 
form pyramids composed of lamince in piles, or bristled with setae or 
tufted filaments of simple ones, and even appear in some cases to 
consist Vvdiolly of hairs. 
Some of the Zootomists, Baron Cuvier in particular, had already 
made known to us the nervous system of various Crustacea of differ- 
ent orders. The same subject has lately been thoroughly examined 
by Messrs. Victor Audouin and Milne Edwards in their third Memoir 
on the Anatomy and Physiology of these animals — Ann. des Sc. Nat. 
XIV, 77, — and all that is now wanting to complete their researches, 
is the ])ublication of those made by M. Straus on the Branchiopoda 
and the Limuli in particular, which they have not noticed. 
“ The nervous system of the Crustacea submitted to our observa- 
tion, say they, presents itself in two very different aspects, which 
constitute the two extremes of the modifications visible in that class. 
Sometimes, as in the Talitrus, this apparatus is constituted by nu- 
merous similar nervous inflations, arranged in pairs, and united by 
cords of communication in such a way as to form two ganglionic 
chains, separated from each other, and extending throughout the 
length of the animal. At others, on the contrary, it is solely com- 
posed of two ganglions or knotty enlargements, dissimilar in form, 
volume, and arrangement, but always simple and azygous, and 
situated, one in the head and the otlxer in the thorax. Such is the 
case in the Maia. 
“ These two modes of organization, at the first glance, certainly 
seem essentially different, and if the study of the nervous system of 
* See the order Decapoda. 
