CHARACTERISTICS OF THE DIGESTIVE APPARATUS. 207 



intestine is short, nearly straight, and simple; sometimes it is also pro- 

 vided with caeca. In insects there is a great variation in the form and 

 length of the canal, depending on the stage of metamorphosis ; nearly 



<§?5& 



Fig. 61.— Digestive 

 Canal of the 

 Leech {Sanguisuga 

 medicinalw), after 

 Nuhn. Fig. 62. ^Viscera of a Caterpillar. {Rymer Jones.) 



oe, (esophagus; v, stom- GH, oesophagus; HI, stomach; IM, intestine; K, biliary vessels ; QR, salivary 



ach; vt, cascal appendages; glands; P, salivary ducts; ABC, tracheaa; D E E E E, air-tubea ; FFF, epiploon, or 

 r t rectum; a, anus. fat-masa; VXT, cieca. 



