2 7 
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 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 Vascular 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. 
