THE AX A TO MY OF IX SECTS. 



part of the digestive system, but are organs of offence, the secretion 

 being acrid or otherwise offensive. 



Insects take the greater part of their food during the larva or 

 nymph state ; for it is in this period that they acquire their growth. 

 In some cases, as with the May-flies and the Bombycid moths, no 

 nourishment is taken during the adult state. With certain larvae 

 (larvae of the higher Hymenoptera, Pupipara, and Ant-lions), the 

 stomach ends blindly, and does not communicate with the intestine. 

 In the Ant-lions the rectum is transformed into a silk gland ; and 

 the silk of which the cocoon is made is spun from the anus. 



The Adipose Tissue. -On opening the body of an insect, especially 

 of a larva, one of the most conspicuous things to be seen is fatty 

 tissue in large masses. These often completely surround the ali- 

 mentary canal, and are held in place by numerous branches of the 

 tracheae with which they are supplied. Other and smaller masses 

 of this tissue adhere to the inner face of the abdominal wall, in the 

 vicinity of the nervous system, and at the sides of the body. It also 

 abounds in the pericardial sinus. In a full- 

 grown larva of Corydalus cornutus I have 

 found the adipose tissue to be greater in bulk 

 than all of the other organs found inside of 

 the muscular walls of the body. In adult in- 

 it usually exists in much less quantity 

 than in lar\ 



The Circulatory System. In insects the 



circulator) system is not a closed one, the blood 



flowing in vessels during only a part of its 



course. The greater part of the circulation 



of this fluid takes place in the cavities of the 



body and its appendages, where the blood 



fills the space not occupied by the intern, il 



The only blood-vessels that exist in 



animals lie just beneath the body-wall, 



above tlie alimentary canal i Fi-. 36, //). They 



id from near the caudal end of the ab- 



into the he. id. 



: of tin i that lies in th 



dom n-t, and con- 



nts of the body (Fig. 40, // 



number <>i" these ch.i . hut it 



May-beetle 



>l aapect <i 

 interior of heart *| 

 valv -..I aspect of 



wing.rauKle* the 

 muscle* ;u. :,d a* 



cut away from the caudal 

 Prt ; ,/, dorsal 



aspect of heart. 



more 



than 



