178 THE MICROSCOPIST. 



place. 4. The small intestine, terminating in 5, the large 

 intestine or colon. The colon of most insects in the 

 imago or perfect state, never in larvae or pupae, contains 

 from four to six organs of doubtful nature arranged in 

 pairs. They are transparent, round, or oval tubercles 

 projecting inside the colon, traversed by tufts of tracheae, 

 and sometimes with a horny ring at the base. 



The salivary glands are sacs or tubes of variable form 

 and length, terminating near the mouth. A distinct liver 

 is absent, its function being performed by glandular cells 

 in the walls of the stomach. Many insects, however, 

 have caecal appendages to the stomach which secrete bile. 

 Some have tubular caeca appended to the small intestine, 

 probably representing a pancreas. In the interspaces of 

 the various abdominal organs, is found a curious organ 

 called the fatty body, which attains its development at 

 the close of the larval period, and appears to form a res- 

 ervoir of nourishment for the pupa. It consists of fat- 

 cells imbedded in a reticular tissue, and is traversed by 

 slender tracheae. 



The Malpighian vessels are slender, mostly tubular 

 glands, caecal or uniting with each other, which open into 

 the pyloric end of the stomach, and as uric acid has been 

 found in them, are thought to serve the functions of a 

 kidney. Some consider the renal organ to be represented 

 by certain long vessels convoluted on the colon, and open- 

 ing near the anus. 



Other glandular organs occur in insects, as cysts in the 

 integument, called glandulae odoriferae ; poison glands, 

 attached to the sting in many females; and silk-secreting 

 glands, coiled in the sides of the body and opening out- 

 side the mouth. 



The heart is a long contractile vessel situated in the 

 back. It is constricted at intervals. The posterior part 

 acts as a heart, and the anterior represents an aorta, and 

 conveys blood to the body. From the anterior end the 



