149 



Acini. — In the granular type of gland the greater 

 portion of the acinus is composed of cells of the 

 character described above. A portion, however, 

 usually exists which differs considerably in struc- 

 ture. This portion adjoins- the duct, and may, in 

 Anophelines, reach as much as one-quarter of the 

 entire gland in length. In this portion of the 

 gland the cells are much smaller than those con- 

 taining the granular secretion, so that the diameter 

 of the acinus is much less here, and a sudden in- 

 crease takes place when the portion containing 

 the granular secretion is reached. The cells 

 lying towards the duct differ from those lying 

 towards the acinar end of this portion. There 

 is, however, no line of demarcation between them, 

 the one gradually becoming changed into the 

 other. In the centre of each cell is a clear body, 

 pushing the nucleus and protoplasm to the outer 

 portion of the cell. Towards the duct end in the 

 centre of this clear substance is a darker portion 

 continuous with the duct lumen. As the cells 

 come to lie nearer the distal portion, this central 

 dark lumen becomes obliterated. This structure, 

 though present in Anophelines, may be absent in 

 Culex. In certain Ciilex another variation in the 

 gland cells frequently occurs. The portion of the 

 gland lying close to the duct, instead of being 

 less in diameter is greater. The cells composing 

 this portion are columnar in shape, with centrally 

 situated nuclei and no contained secretion. 



In certain specimens it is not uncommon to 

 find cells occupying a peripheral position, and not 

 approaching the lumen, which contain a substance 

 resembling the colloid-like secretion of the clear 

 type of gland. 



