120 MEDICAL ENTOMOLOGY 



of reaction than by any actual dimunition in the number of bites 

 inflicted. 



A similar idiosyncrasy is to be noticed with regard to other insects. 

 Many people suffer acutely from the bites of Tabanids, which in 

 the majority of cases produce only a momentary irritation and some 

 rubifaction. The same thing has been noticed with Simulium. 



The salivary glands of the Diptera are usually tubular and elongate, 

 though great variation in their length is met with in the order. The 



blind end is often a little dilated, giving it a saccular 

 The Glands ... 



appearance, and possibly enabling it to retain a quan- 

 tity of saliva. The glands may extend through the thorax, and be 

 twisted into many convolutions on account of their length, or they 

 may be confined to the anterior part of the thorax. The increase 

 in the length of the glands corresponds with other anatomical points 

 which indicate a high degree of specialization. For instance, in 

 Phlebotomus they are short and round, while in Glossina they are 

 extremely long. The increase in length gives, of course, a greater 

 extent of secreting surface, as was pointed out in connection with 

 the alimentary canal. 



The salivary glands of mosquitoes are of particular importance 

 since it is in them, in certain species of Anopheles, that the parasite 



of malaria is to be found previous to its entrance into 

 Culex and Anopheles 



the blood of man. They are of the tubular type, and 



are confined to the thorax of the insect. Certain differences between the 

 glands in Anopheles and Culex (Plate XXVII, figs. 7 and 8) have been 

 emphasized by Christophers and by Nuttall and Shipley. 



There are three glands on each side, lying in the lower part of the 

 anterior end of the thorax, immediately above the first pair of legs. 

 They are just below the main mass of thoracic muscle, and lie embedded 

 in fat body. The ducts meet in a common point as they emerge from 

 the substance of each gland, and lead by a common duct to the neck, 

 where those of the two sides unite in the region of the occiput, and 

 under the sub-oesophageal ganglion, to form a single channel, which 

 passes to the salivary pump described in connection with the mouth 

 parts. 



Each acinus is an elongate tubule, within which, in the fresh state, the 

 intra-acinar duct can be seen. Of the three acini on each side the one 

 which lies between the others, and appears dorsal to them in cross sec- 

 tions of the anterior part of the thorax, is slightly smaller than its fellows. 

 All the glands consist of a single row of cubical or short columnar cells 



