COMMON COCKROACH. 139 



adult state, have been removed, and the digestive tract fastened out upon 

 the left side of the body. 



The digestive tract is divisible into three regions, which correspond to 

 the stomodaeum, archenteron, and proctodaeum of the embryo. The first 

 of these includes oesophagus, crop and gizzard, the second, the chylific 

 stomach and caeca, and the third, the intestine and rectum. The narrow 

 oesophagus expands directly into the crop, which occupies about three- 

 fourths of the entire length of the body, and is distended with food. The 

 digestive tract as a whole, however, is little more than twice as long as the 

 body, a comparative shortness compensated partly by the character of the 

 food, and partly by the large quantities devoured. A muscular subconical 

 gizzard follows the crop. This organ is not developed in the larvae of In- 

 secta with a perfect metamorphosis, e. g. Coleoptera, in those species which 

 possess it when adult, but is developed in larval Orthoptera as well as 

 Odonata. The posterior end of the gizzard is elongated and projects into 

 the chylific stomach. Eight ' pyloric ' caeca arranged in a whorl mark 

 the commencement of this region, and a very much larger number of long 

 and slender Malpighian or renal tubes its termination. Pyloric caeca are 

 found in most Ort/wptera, and in the Plecoptera. Their walls are glandular, 

 and the size of the caeca varies with their state of distension. The intestine 

 consists of a short, narrow ' ileum,' and a long, somewhat dilated colon. The 

 ileum is not clearly visible in this preparation. The colon is ridged and 

 beaded owing to the contraction of its muscular coats. It ends in a rectum, 

 which shows six longitudinal ridges alternating with furrows. 



The lobed labial salivary glands are to be seen on either side of the 

 anterior end of the crop : and on the right side in this preparation the right 

 salivary receptacle, a pellucid bladder reaching a little further back than 

 the gland. 



An azygos nervus rectirrens, derived from the 'ganglion impar' or 

 ' frontale ' of the stomatogastric system, lies on the dorsal wall of the crop, 

 and ends in a triangular ganglion placed a little way in front of the middle 

 point of its length. From this ganglion a nerve may be traced passing 

 down the sides of the crop to the gizzard. The paired ganglia of the system 

 are not to be seen. The six terminal ganglia of the ventral chain are visible 

 in the abdomen. The two first are more closely apposed to each other than 

 are any of the succeeding four. The last ganglion is more or less cordiform, 

 larger than those which precede it, and gives off nerves to the lower por- 

 tion of the digestive and generative tubes. 



Each ovary consists of eight ovarian tubes or ovarioles inserted in 

 pairs, on the inner edge of the oviduct, one set of tubes along its ventral, 

 the other on its dorsal margin. The tubes are beaded, owing to the 

 swellings caused by the ova. These ova increase in size the nearer they 

 are to the oviduct. The tips of the ovarioles are in the natural state united 



