142 



Heidenhain's haematoxylin gives good results 

 with the salivary glands, and also the muscle 

 fibres in connexion with the alimentary canal. 



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 membrane 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 pupa, the oesophageal diverticulum is 

 seen passing backwards as a narrow tubular organ 

 lying beneath the mid-gut. It is in this stage 

 lined with well-marked cubical epithelium. In a 

 freshly-hatched mosquito this organ is frequently 

 undistended, and shows anarrow lumen surrounded 

 by a single layer of large cells. These cells re- 

 tain very little trace of protoplasm, which, how- 

 ever, may still be present in fine strands, and 



