186 rHYSTOLOGY OF INSECTS. 



double or duplex when it is divided into two distinct por- 

 tions, one preceding the other : in this instance the anterior 

 portion seems to be the principal organ of digestion, and in 

 form, as well as office, frequently appears to resemble the 

 gizzard of birds : the posterior portion corresponds with 

 the stomach in its usual simple form. The stomach is tri- 

 ple or triplex when it possesses three separate divisions fol- 

 lowing each other longitudinally ; it sometimes, but rarely, 

 has four or more of these divisions : and finally, it is called 

 compound or compositus when it throws off two or more 

 minor stomachs or cceca, resembling little purses, at or 

 near its union with the gidlet ; these are particularly obser- 

 vable in the voracious herbivorous insects, which have the 

 anterior portion of the stomach in the form of a gizzard. 



The stomach varies also in the character of its interior 

 surface ; it is sometimes perfectly smooth, and sometimes 

 covered with a pilosity more or less shaggy ; this pilosity 

 has been said to consist of minute tubular processes, which 

 secrete the fluid for digestion. 



The stomach, at its posterior extremity, unites with the 

 intestines; these consist of two portions, the small intes- 

 tines or intestina parva, and the terminal intestine or 

 rectum. 



The whole of the alimentary canal, from its anterior to 

 its posterior opening, is frequently httle more than a direct 

 tube or cylinder ; the intestines are never subject to the 

 convolutions so general in vertebrated animals ; the pas- 

 sage of the food is excessively rapid, and the change it 

 undergoes very slight. There are, originating from the 

 stomach, at or near its union with the intestines, several 

 long tortuous filiform appendages, which are said to be bile 

 vessels, and to correspond with the liver of vertebrated 

 animals. 



Organs of Circulation. — In vertebrated animals the heart 



