18 
Guide to Crustacea . 
Wall- 
cases 
Nos. 1 -i 
It is divided into two chambers, a larger one in front, the “ cardiac 
chamber,” which serves as a kind of crop, and a smaller “ pyloric 
chamber ” behind. In the narrow opening between the two 
chambers are set three strong teeth which are connected with a 
system of plates and levers lying in the stomach- wall and moved 
by special muscles. This development of hard plates and teeth is 
associated with the fact that the whole stomach is lined by a 
membrane continuous at the mouth with that which covers the 
surface of the body and becomes thickened and hardened to form 
the shell. The external membrane also becomes turned in at the 
vent to line a considerable part of the intestine. 
On each side of the thoracic region of the body is a large 
Fig. 4. 
Dissection of male Lobster, from the side. [Wall-case No. 1.] 
glandular mass, the “liver” or digestive gland, which opens into 
the alimentary canal by a short duct on each side just behind the 
stomach. 
The heart lies near the back, just under the hinder part of the 
carapace. It gives off a number of large arteries in front and 
behind, as well as one (“ descending artery ”) which runs down- 
wards to the sternal surface of the thorax. As in other Arthro- 
poda, there are no distinct veins, but the blood is discharged from 
the smaller arteries into the general cavity of the body and finds 
its way by ill-defined venous channels, first to the gills, and from 
these to the “ pericardium ” or space surrounding the heart. From 
the pericardium the blood returns through six valvular openings 
into the heart itself. 
The excretory system (corresponding in function with the 
