52 THE PHYSIOLOGY OF THE COMMON CRAYFISH. 
gullet opens, and a small posterior chamber (ps), from 
which the intestine (hg) proceeds. 
In a man’s stomach, the opening by which the gullet 
communicates with the stomach is called the cardia, 
while that which places the stomach in communication 
with the intestine is named the pylorus ; and these terms 
having been transferred from human anatomy to that of 
the lower animals, the larger moiety of the crayfish’s 
stomach is called the cardiac division, while the smaller 
is termed the pyloric division of the organ. It must be 
recollected, however, that, in the crayfish, the so-called 
cardiac division is that which is actually furthest from 
the heart, not that which is nearest to it, as in man. 
The gullet is lined by a firm coat which resembles thin 
parchment. At the margins of the mouth, this strong 
lining is easily seen to be continuous with the cuticular 
exoskeleton; while, at the cardiac orifice, it spreads out 
and forms the inner or cuticular wall of the whole gastric 
cavity, as far as the pylorus, where it ends in certain 
valvular projections. The chitinous cuticle which forms 
the outermost layer of the integument is' thus, as it were, 
turned in, to constitute the innermost layer of the walls 
of the stomach; and it confers upon them so great an 
amount of stiffness that they do not collapse when the 
organ is removed from the body. Furthermore, just as 
the cuticle of the integument is calcified to form the hard 
parts of the exoskeleton, so is the cuticle of the stomach 
calcified, or otherwise hardened, to give rise, in the first 
