133 



anterior ends lying close against the prosternum, 

 wliere the ducts coming from each acinus unite to 

 form a single duct. The upper and middle acini 

 generally lie with their distal ends close to the 

 proventriculus. The lower acinus passes towards 

 the thoracic ganglion. Occasionally, an acinus 

 becomes bifid at a short distance from its termina- 

 tion. A common abnormality also, is a small 

 accessory acinus near the proximal end of an 

 acinus. A duct can be seen traversing almost the 

 entire length of each acinus. Shortly after leaving 

 the acinus, the three unite to form a single duct. 

 The duct of each side passes up into the neck, and 

 lies close to the nerve cords passing between the 

 thoracic and thecerebral ganglia. Beneath, and in 

 contact with the lower surface of the suboesopha- 

 geal ganglion, the ducts of each side unite to form 

 a common salivary duct which passes forwards 

 and enters the chitinous first portion of the 

 alimentary canal close to the base of the proboscis 



(Fig- 34)- 



The Malpightan Tubules. — These are five in 



number and open into the first portion of the hind- 

 gut immediately beyond the pylorus. Their blind 

 ends are held in position in the neighbourhood of 

 the rectum by tracheal branches. They pass 

 forwards in loops above their origin, so that, in 

 transverse section, as many as ten may be seen 

 cut across. 



The Muscular System 



The chief muscular masses in the mosquito 

 are coritained in the thorax. They are chiefly 

 muscles moving the wings and legs. 



Wing Muscles. — There are two large muscular 



