1338 



CRUSTACEA. 



mach, is invariably torn off, not far from the base of the oesophagus, as 

 in the figure. 



The stomach has a broad cordate form, and is a little shorter than 

 the oesophagus, and when expanded is somewhat wider than long ; 

 vertically it is quite narrow. The anterior extremity lies between 

 the prehensile legs, and posteriorly it extends under the furcate pro- 

 cess on the venter. The lateral margin is very deeply crenated, 

 owing to the peculiar arrangement of its muscles. The teguments of 

 the stomach are composed of the same coats as the oesophagus, and 

 they present the same general character. The inner appears uni- 

 formly smooth and even. The outer contains several muscular bands, 

 which connect the opposite crenations : in their contraction the crena- 

 tions are rendered more prominent. These muscles are connected by 

 other slender muscles, irregularly arranged, which contract the sto- 

 mach longitudinally. The lateral portions of the stomach are con- 

 nected on each side with the shell adjoining, by ligamentous attach- 

 ments, as is represented in fig. h. There is no valve between the 

 stomach and the intestine, and when the peristaltic motion is reversed, 

 as often happens, the fluids frequently return into the stomach. 



The intestine, at its commencement, is between three and four 

 times the diameter of the oesophagus, and about one-fifth the diameter 

 of the stomach. It is slightly enlarged below the second pair of nata- 

 tories, where there are two pairs of glands, contracts again as it passes 

 below the apron, and thence continues of uniform size to the rectum. 

 Its structure is very similar to that of the stomach, both in its inner 

 and outer coat. The arrangement of its muscles in regular bands is 

 represented in fig. m; during their action the canal is crenated, as in 

 the figure. The intestine is attached by distinct ligaments at several 

 places ; near the glands, d, and the glands, e and f, we have distinctly 

 seen these attachments. 



The rectum occupies the terminal half of the last abdominal seg- 

 ment, and is about one-half the diameter of the intestine. Its com- 

 munication with the intestine is closed, in the natural state of the 

 parts. This rectum, if it may be so called, appears to have a longi- 

 tudinal opening below, extending its whole length, and its walls are 

 usually in close contact. The external opening or anus is situated at 

 its extremity. 



This portion of the alimentary canal is opened laterally by seven 

 pairs of slender muscles. The first pair, at the extremity, pass directly 



