DIGESTIVE SYSTEM 161 



respectively of the embryo ; and the mesenteron, or 

 middle portion, which alone is formed from the 

 primitive alimentary tract of the embryo. 



a. The stomatodceum has a chitinous cuticular lining, 

 continuous with the cuticular investment of the 

 head ; and is divided into the following regions. 

 i. The buccal cavity is lodged in the head, and its 

 posterior wall is raised up to form an elongated 

 fleshy tongue or lingua. 



The salivary duct opens by a median 

 aperture in the angle between the lingua and 

 thelabium (fig. 30). 



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-w T alled pyriform sac, 

 extending through the thorax and far into 

 the abdomen. It is not separated by any dis- 

 tinct 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 

 them six small elevations covered with setae. 



Lay the gizzard open to expose the teeth. 



FIG. 30. Periplaneta americana. The male dissected from the right 

 side. The testes, which are very small in the adult, are not 

 figured, (c. H. H.) 



A, anus. AN. antennary lobe of supra-cesophageal ganglion, with anten- 

 nary nerve cut short. C, crop. CG, supra-oesophageal ganglion. CL, colon. 

 CK, anal cercus. CX, coxa. E, elytron. F, lemur. FG, frontal ganglion. 

 FN, visceral nerve. G, gizzard. GP, one of the gonapophyses. G5, fifth 

 abdominal ganglion. H, hepatic caecum. HT, heart. I, ileum. L, lingua. 

 LN". nerve to labrum. LP, labial palp. M, mushroom-shaped gland. 

 MC, Malpighian cascaopeninginto junction of mesenteron and ileum : they are 

 much longer and more numerous than indicated. MD, duct of mushroom- 

 shaped gland. ME, mesenteron. MN, maxillary nerve. MP, maxillary 

 palp. PN, labial nerve. PP, podical plate, diagrammatically drawn. R, rec- 

 tum. S, sub-o3sophageal ganglion. SD, salivary duct just above its opening 

 into the mouth. SG, salivary glands. SL, style borne by ninth sternum. 

 SR, salivary receptacle. ST, one of the abdominal stigmata. T, proximal 

 joint of the tarsus. TB, tibia. TR, trochanter. Tl. first thoracic tergum, 

 or pronotum. T3, third thoracic tergum, or metanotum. VG, visceral ganglion. 

 "W, wing. 2, tergum of second abdominal segment. 8, tergum of eighth 

 abdominal segment. 



M 



