PHYSIOLOGY OF THE INVRRTEBRATA. 95 



lluicls within this organ are always slightly alkaline, and an 

 infusion of about twenty of these organs readily converted 

 starch into glucose, and digested fibrin. 



(/>) The Lcpidoptcra. — As an example of this important 

 order we describe the physiology of the alimentary canal of 

 the larva and imago of Pontia hrassiccc (the large white 

 cabbage butterfly). 



The alimentary canal of the larva (Fig. 26, a) agrees 

 closely with the general Lepidopterous type. The mouth 

 opens into a pharynx lined by a dark, firm cuticula, and into 

 the latter open two ducts from a pair of well-developed 

 salivary glands. These glands form elongated tubes, gra- 

 dually diminishing in diameter towards the posterior ends. 

 The oesophagus is very narrow and short. It leads into a 

 long chylitic stomach, which opens into a short duct. Behind 

 the stomach the intestine consists of four parts : first, a short, 

 constricted piece ; second, a dilated, oval division ; third, the 

 short rectum ; and fourth, the anal tube. The stomach has 

 an epithelium lining, which is thrown up into folds so as to 

 form imperfectly differentiated glandular follicles. 



At the posterior end of the stomach are the Malpighiau 

 tubules. 



Fig. 26, B, represents the alimentary canal of the imago of 

 Pontia. The pharynx passes into a narrow, but long, oeso- 

 phagus leading to the crop or food receptacle. 



This crop is entirely absent in the larval, but is developed 

 in the pupal stage. The stomach is much smaller than in 

 the larva, but its lining is also thrown up into glandular 

 follicles. The posterior end of the stomach leads into a long 

 and peculiarly coiled small intestine. The intestine passes 

 into the wide terminal division, the rectum, from the front 

 end of which there is a curved blind c£ecum or pouch. 



In the imago of Pontia there are also a pair of well- 

 developed salivary glands. 



The secretion of the salivary glands is alkaline to test- 

 papers, and readily converts starch into glucose. It has. 



