123 
preparations. The tissues are best dissected out in 
saline of low tonicity, 0*3 or 0*4 per cent., as insect 
juices have a lower isotonic point than those of mam¬ 
mals. 
The Histology of the Alimentary Canal and 
Appendages 
The epithelial lining differs considerably in the 
mid-gut from either the fore-gut or hind-gut. In 
the mid-gut the possession of a marked striated border 
by the epithelial cells is characteristic. The muscular 
fibres of the alimentary canal are striated throughout. 
The Fore-gut .—The anterior portion of the fore¬ 
gut is lined by chitin and does not differ from the 
cuticle in structure. It consists of a single layer of 
cubical cells of small size. The oesophageal dilatation 
and its diverticula resemble one another in structure. 
In the adult mosquito they consist of an extremely 
delicate membrane formed of a single layer of flattened 
cells, with externally some scattered muscular fibres. 
In fresh preparations peculiar wrinklings of this mem¬ 
brane are seen, which may appear like bundles of 
sporozoits. A similar appearance is seen in the dilated 
portion of the hind-gut just beyond the pylorus. 
In the majority of mosquitoes the walls of the 
oesophageal diverticulum are crowded with micro¬ 
organisms and bodies which appear to be protozoal in 
nature. 
The Mid-gut .—The epithelium consists of a single 
layer of large cells, which are columnar in the undis¬ 
tended organ, but become flat and pavement-like when 
the organ is full of blood. They have a finely- 
reticulated protoplasm, which stains more deeply 
towards the free border. Stained with Heidenhain’s 
