42 PHYSIOLOGY OF THE INVERTEBRATA. 



In Blatta the moutii leads into an oesopliagus wliich gradu- 

 ally dilates into a large crop (ingluvies). The crop passes 

 into a small gizzard or proventriculns, and then into a 

 wide tubular stomach, the so-called chylific ventriculus, which 

 leads into the small intestine or ileum, followed by the large 

 intestine or colon, and the rectum; the latter terminating 

 in the anus, which is situated between the podical plates. 

 To the anterior end of the stomach are attached seven or 

 eight pyloric caeca ; and from the posterior end of the 

 stomach are several Malpighian or urinary tubules (from 

 twenty to thirty). The mouth of Blatta, which has a ventral 

 aspect, is provided with a pair of well -developed salivaiy 

 glands and receptacles. Each gland is divided into two 

 lobes composed of numerous acini. The proventriculus con- 

 tains six principal teeth, and between each pair of teeth are 

 five smaller teeth. These teeth or ridges are produced by 

 the folding of the chitinous lining of the crop, which passes 

 into the proventriculus. The ileum is separated from the 

 large intestine or colon by a circular valve ; and the walls of 

 the rectum are raised into six ridges projecting into the 

 interior. These ridges are the rectal glands. 



The mouth of Blatta is situated between " the labrum in 

 front, the mandibles and maxillae at the sides, and the 

 labium, with the large lingua, or hypopharynx, behind." In 

 all the Orthoptera the mouth is constructed on the above 

 plan, but the Physopoda* '' present a modification which is 

 transitional to the Hemipteran mouth. There is a proboscis 

 directed backwards, and formed by the union of the labrum 

 with the labium, which last is provided with palps, though 

 they are sometimes very small." 



The labrum, labium, mandibles, and maxillae of the Insecta 

 are, in the main, subservient to the functions of taking in or 

 crushing food. In the carnivorous Lihellula depressa, the 

 alimentary canal is short and there is neither crop nor gizzard, 

 but the so-called chylific ventriculus is present, 

 * A sub-order to which Thrips belongs. 



