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 



