The Cockroach. 55 



The alimentary canal is rather complicated. As in the 



"■■ crayfish, there is a large anterior section lined with chitin, and 



■!■! termed the stomodseum ; a large posterior section, also lined 



with chitin, and ternied the proctodaeum ; and a short middle 



;; section, the mesenteron. The mouth leads through a short 



" oesophagus, gradually widening into a large crop ; this is 



followed by a thick-walled gizzard, with six large cuticular 



teeth. Then follows the short mesenteron. The proctodseum 



is divisible into a short ileum, a long colon, and a wide terminal 



rectum whose inner walls are raised into a number of ridges. 



The alimentary tract is furnished with a number of glands. 



Firstly, the salivary glands, which are present on each side 

 of the crop to the number of two. They are white diffuse 

 glands, and between them lies a bladder, the salivary receptacle. 

 The ducts of all unite to open into the mouth cavity. Opening 

 into the mesenteron (sometimes called the " chylific stomach ") 

 are the hepatic cceca, blind tubes, seven or eight in number. 

 Finally, there are the malpighian tubes, sixty or more, which 

 open into the commencement of the intestine. These, how- 

 ever, are not glands supplying any fluid used in digestion ; 

 they are excretory in function, and uric acid has been found 

 in them. It is doubtful whether these structures can be com- 

 pared with the excretory organs of other animals. There are, 

 however, a few facts which render a comparison possible (see 

 p. 158). But it is necessary, in the mean time, to dwell rather 

 upon their unlikeness to the excretory organs of other animals. 

 The nervous system is constructed precisely on the plan of 

 that of Astacus. There is a supracesophageal ganghon con- 

 nected by a circumcesophageal commissure with a ventral 

 chain of three thoracic and six abdominal ganglia, besides a 

 suboesophageal ganglion in front, which seems to represent 

 three fused ganglia, as it supplies the three first postoral 

 pairs of appendages. There is also a visceral nervous system, 

 consisting of a small frontal ganglion, which is connected with 

 the circumcesophageal commissure by two nerves, and which 

 gives off backwards a single nerve, running back along the 

 crop to a small ganglion on the dorsal surface of the crop, 

 whence two nerves run still further back. 



