THE (ESOPHAGUS, STOMACHS AND INTESTINES. 407 



3. THE (ESOPHAGUS, STOMACHS AND INTESTINES, AND 

 THEIR ACCESSORY GLANDS. 



a. The Alimentary Tract (Plate XXIV.). 



The oesophagus, crop, proventriculus, chyle stomach, proxi- 

 mal intestine, distal intestine, and rectum constitute the 

 alimentary tract. 



The oesophagus commences at the posterior extremity of the 

 fulcrum, and, curving sharply backwards, passes between the 

 supra- and infra-cesophageal nerve-centres and through the 

 cephalo-thoracic opening ; above the great nerve-trunk and 

 beneath the dorsal vessel and median splanchnic nerve, which 

 are in relation with it. 



In the thorax it lies upon the thoracic nerve-centre and 

 the metasternal entothorax, immediately beneath the chyle 

 stomach, with the coiled salivary glands on either side of it. 

 It passes back into the abdomen and enters the great pyriform 

 bi-lobed crop. 



Immediately below the proventriculus, it gives off a short 

 vertical tube, the proventricular oesophagus, which enters that 

 organ and transmits the food to the chyle stomach. 



The Crop (PI. XL, s s) occupies a considerable portion of the 

 base of the abdomen, and lies behind, below, and between the 

 great abdominal pulmonary sacs (PI. XL, p s). 



Structure. The muscular coat of the oesophagus is thicker 

 than that of the rest of the alimentary canal, and both the 

 longitudinal and circular fibres are well striated, and resemble 

 those of the ordinary skeletal muscles ; the muscle fibres of 

 the crop are indistinctly striated, and are flattened bands 

 which anastomose with each other, and present large meshes 

 when the organ is distended. 



The epithelium of both consists of thin pavement cells ; the 

 cuticular intima is very thick in the oesophagus, and is thrown 

 into permanent longitudinal folds, into which the epithelial cells 

 penetrate as they do in the crop of the larva. The cuticle of 

 the crop is thin, and does not exhibit any distinct infoldings. 



