ANNULOSA: INSECTA. 



'37 



mitted to a second muscular stomach, called the " gizzard " (fig. 

 82). The gizzard is adapted for crushing the food, often hav- 

 ing plates or teeth of chitine developed in its walls, and is suc- 

 ceeded by the true digestive 

 cavity, called the "chylific sto- 

 mach " (vcntriculus chylopoieti- 

 cus}. From this an intestine 

 of variable length proceeds, its 

 terminal portion, or rectum, 

 opening into a dilatation which 

 is common to the ducts of the 

 generative organs, and is termed 

 the "cloaca." The oesophagus 

 is furnished with salivary glands 

 of varying size and complexity, 

 and is provided in some of the 

 Suctorial Insects with a dilata- 

 tion called the "sucking sto- 

 mach." Behind the pyloric 

 aperture of the stomach, with 

 very few exceptions, are a vari- 

 able number of caecal, convolu- 

 ted tubes (fig. 82, e), which 

 open into the intestine, and are 

 called the "Malpighian tubes." 

 These are often looked upon 

 as representing the liver, but 

 are by some believed to have a 

 renal function. If the Malpig- 

 hian vessels truly perform the 

 functions of a liver as their 

 position would appear to prove then the kidneys will be repre- 

 sented by a series of csecal tubes which are only occasionally 

 present, and which open into the rectum, close to the cloaca. 

 There are no absorbent vessels, and the products of digestion 

 simply transude through the walls of the alimentary canal into 

 the sinuses or irregular cavities which exist between the abdom- 

 inal organs. The apparatus of digestion does not differ essen- 

 tially from the above in any of the Insects, but the alimentary 

 canal is, generally speaking, considerably lengthened in the 

 herbivorous species. 



There is no definite and regular course of the circulation in 

 the Insects. The propulsive organ of the circulation is a long 

 contractile cavity, situated in the back and termed the " dorsal 

 vessel." This is composed of a number of sacs (ordinarily 



Fig. 82. Digestive system of a Beetle 

 (Carabus auratiis), a (Esophagus ; b 

 Crop ; c Gizzard ; d Chylific stomach ; 

 e Malpighian tubes; /Intestine; ^Clo- 

 aca ; h Supposed renal vessels. 



