127 



In Anopkelines 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 Malpighian Tubules. The malpighian tubules 

 are tubular bodies with caecal ends, which open into 

 the hind-gut. The cells are extremely large, being, 

 next to the pericardial cells, the largest in the body. 

 Each cell contains a large nucleus, and contains 

 numerous large granules which stain feebly with 

 haematein, but powerfully with Heidenhain's haema- 

 toxylin. Numerous fatty granules are also present. 

 Each cell is wrapped round a central lumen, the cells 

 being arranged alternately, so that a zig-zag appear- 

 ance is given in section. The inner portion of each 

 cell is markedly striated, the lumen being thus 

 bounded by a striated area. In relation with these 

 tubules, a large number of tracheae and tracheal 

 end-cells exist. 



In certain conditions the malpighian tubule cells 

 may be found quite free from granules, though other- 

 wise unchanged. This change occurs in mosquitoes 

 with large numbers of flagellates in the rectum and 

 hind-gut. 



The V ascular System. The dorsal vessel is a 

 delicate-walled tube composed of longitudinal and 

 oblique fibres with a nucleated inner layer. The fibres 

 may be traced directly from the terminations of the 

 branched alary muscle fibres. The alary fibres break 

 up into fibres which pass in close connexion with the 

 large pericardial cells, and eventually form (i) fibres 

 passing into the dorsal vessel as longitudinal fibres, 

 (2) fibres joining in an anastomosis in connexion with 

 the floor of the dorsal vessel. 



