ALIMENTARY TRACT OF MOSQUITO 10$ 



the exception of Phlebotomus, they have not been studied very closely, 

 but so far as our knowledge goes they conform generally to the type 



seen in Tabanns. The proventriculus does not ap- 



.... . . . . , Other Orthorraphic 



pear to be so well developed in any of them as it is F|j 



in the latter, the oesophagus passing downwards as 

 a simple tube to merge with the mid-gut. The digestive epithelium 

 commences some distance anterior to the dilated part which is evid- 

 ently mid-gut. The Malpighian tubules vary in their number and 

 mode of origin. In Culicoides (Plate XXII, fig. 3) there is only one 

 pair, but these are very thick, and are very conspicuous in dissections 

 on account of their dead white colour, which is quite different to that of 

 the hind-gut. In Simiilium there are two pairs which arise from a very 

 short common stem, and in Phlebotomus (Plate XXII, fig. 4) two pairs 

 arising from a much longer common portion ; of the two on each 

 side one is considerably longer than the other ; both terminate in slightly 

 swollen ends. 



The crop is very well developed in Phlebotomus ; its duct, which is 

 an extremely fine one, leaves the oesophagus a little in front of the 

 nape of the neck (Newstead). In Culicoides and Simiilium it is 

 not quite so large, but in none of them is it so closely connected with 

 the oesophagus as it is in the Culicinae. It appears to function in 

 a slightly different way to that of Tabanus, for both in Phlebotomus 

 and in Culicoides it is found distended with blood in flies killed 

 immediately after feeding, while a few hours later it is empty or nearly 

 so. Apparently the blood is received into it from the pharynx, and 

 passed on to the mid-gut gradually, as fast as it can be digested. 

 The mid-gut, like that of Tabanus, is capable of very great distension. 



The alimentary canal of the mosquito, like the rest of its anatomy, 

 presents considerable modifications from the other Orthorrapha. 

 The differences in the various genera, however, are not important, and 

 for practical purposes all may be included in one description. 



The oesophagus is a short and thin-walled tube which passes from the 

 posterior end of the pharynx in the head to the anterior part of the 



thorax, where it joins the mid-gut. The two are 



The Mosquito- 

 separated, however, by a valvular structure believed to Oesophagus 



be the homologue of the proventriculus. The wall is 

 composed mainly of a single layer of flattened epithelial cells, with in- 

 determinate boundaries and small oval deeply staining nuclei. Internal 

 to this there is a thin chitinous intima, most marked in the anterior 

 portion of the tube, where it is provided with a set of fine spicules 



