DIGESTIVE SYSTEM. 179 



ii. The oesophagus is a narrow tube running from 

 the mouth through the nerve-collar and along 

 the neck. It is laterally compressed in the 

 cervical region. 



iii. The crop is a large thin-walled pyriform sac, 

 extending through the thorax and far into the 

 abdomen. It is not separated by any distinct 

 line of demarcation from the oesophagus. 



iv. The gizzard, or proventriculus, is a pyriform sac, 

 with thick muscular walls. Within it is a 

 series of six large cuticular teeth, and behind 

 these six small elevations covered with setae, 

 which serve as a strainer. 



Lay the gizzard open to expose the teeth. 



b. The mesenteron is a short narrow tube extending 



backwards from the hinder end of the gizzard. 



Lay the mesenteron open, and note the funnel-like prolon- 

 gation of the gizzard extending into it. 



c. The proctodceum is the convoluted hinder portion 



of the alimentary canal, and is lined by a thin 

 chitinous cuticle. It is divided into the following 

 regions : 

 i. The ileum is a short narrow tube, the commence- 

 ment of which is marked by the attachment 

 of the numerous fine thread-like Malpighian 

 tubules. 



ii. The colon is much wider and longer than the 

 ileum, and is constricted at its hinder end. 



iii. The rectum is the short dilated terminal portion 

 of the alimentary canal. Its wall has six longi- 

 tudinal ridges, projecting internally. It ends 

 at the anus, between the podical plates. 



2. The digestive glands. 



a. The salivary glands are two pairs of diffuse white 

 glands on the sides of the anterior part of the crop. 



