148 



distinct as in the granular type, and the secretion, 

 when extended by pressure, is much less refractive. 

 In alcohol-hardened specimens, the acinar cells 

 contain a large mass of clear, homogenous .secre- 

 tion which, as in the last-mentioned type, fills 

 almost the entire cell, and pushes the protoplasm 

 and nucleus to the periphery. 



In the clear type, however, the protoplasm is 

 always in greater amount than is the case with 

 the granular type, and the nucleus never becomes 

 so greatly degenerated. The clear, homogeneous 

 secretion stains readily with haematein, and may 

 even stain quite deeply. With Heidenhain's 

 haematoxylin it frequently becomes almost black. 

 It resembles very much in appearance colloid 

 substance as it is seen in the mammalian thyroid. 



In Anophelines this substance also distends the 

 central duct space within the acinus. In this 

 situation an appearance is sometimes produced 

 which resembles faintly-stained sporozoits, but 

 which is a normal condition. 



The Maturation of the Glands. — In freshly- 

 hatched mosquitoes both types of acinus consist 

 of large glandular cells arranged round the lumen. 

 These contain a large, centrally situated nucleus, 

 and have protoplasm containing a large number 

 of coarse granules, staining with haematein. In 

 the portion of the cell nearest the lumen a vacuole 

 of varying size is situated. This is the commence- 

 ment of the large mass of secretion which, in the 

 mature gland, occupies the entire cell. In the 

 granular type of acinus the vacuole contains 

 granules ; in the clear type it resembles the colloid- 

 like secretion (Fig. 36). 



Further Variations in the Cells of the Salivary 



