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 pyloras ; 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 margms 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 laj^er of the walls 

 of the stomach ; and it confers \\\)o\\ them so great an 

 amount of stiffness that they do not collapse when the 

 organ is removed from the bod}'. 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 



