146 



similar to that of the mid-gut, consisting of very 

 large fusiform, straited cells arranged circularly 

 and longitudinally. The circular fibres in the 

 small intestine lie outside the longitudinal, and 

 pass spirally around the mid-gut. Towards the 

 termination of the intestine longitudinal fibres 

 also lie outside the circular. In the rectum and 

 extending throughout the hind-gut and mid-gut 

 in the Culicidae, there are, in a large proportion 

 of specimens, swarms of a flagellate organism 

 (Fig. 40). 



The Salivary Glands. — The salivary acini lie 

 in a cleft in the fat-body, which latter comes in 

 close contact with the glands. Each gland acinus 

 consists of a single layer of large cells, limited 

 externally by a delicate sheath (basement mem- 

 brane) and internally by the intra-glandular duct 

 wall. 



In Anophelines the intra-glandular duct 

 becomes larger as it approaches the termination 

 of the acinus, and forms a large cavity. 



In Culicines the duct remains of the same dia- 

 meter throughout the acinus, and terminates 

 abruptly near the end of the acinus without any 

 dilatation. 



In both Culicines and Anophelines there are 



two types of gland acinus. These are recognizable 



both in the fresh gland and in fixed specimens. 



From their appearance in the latter they may be 



termed / x ^, , 



(i) 1 he granular type. 



(2) The clear or colloid-like type. 



The Granular Type — The greater portion of 

 the acinus consists of cells whose nucleus and 

 protoplasm has been pushed to the outer portion 



