516 MEDICAL ENTOMOLOGY 



the broad end being directed forwards ; after the discharge of their 

 contents they lose their tense and rounded appearance, and become 

 a little elongated. The wall consists of a single layer of flattened cells, 

 with some fine muscle fibres. They lie free in the haematocoele, 

 and when the thorax and abdomen are drawn apart, as in the method of 

 dissection to be described presently, the two glands generally slip out 

 through the rupture in the body wall. A fine duct with a ringed chitin- 

 ous intima, like that found in the salivary ducts in the Diptera, emerges 

 from the broader anterior end, and passes forwards for a distance less 

 than the length of the gland ; it then divides, the two resultant ducts 

 being, as Landois pointed out, only half the thickness of the common 

 duct, suggesting that saliva flows through both channels. One of 

 these two ducts can be traced without much difficulty through the 

 neck to the salivary pump in the head, near which it unites with its fel- 

 low of the opposite side to enter the pump in the middle of its ventral 

 surface. The other duct has not been followed to its destination by the 

 present writers. Landois states that it passes first forwards, then bends 

 again backwards towards the abdomen, reaching the anterior region of 

 the stomach, and finally bends again forwards, to open into the stomach 

 near its junction with the oesophagus a remarkable mode of termination 

 for a salivary duct. 



These glands are held in position by an arrangement of fine fibres 

 which are inserted, according to Landois, in the integument of the head. 

 The fibres arise from the whole surface of the gland, and are collected 

 together to form a fine cord at the inner side of the common duct at its 

 origin from the gland. The suspensory cord is very easily ruptured if 

 the head is pulled away from the thorax, and has not nearly as much 

 resistance as the duct, a point which throws some doubt on the function 

 assigned to it. It seems more probable that the muscle fibres in the cord, 

 spread out as they are over the whole surface of the gland, serve to com- 

 press it when the saliva is to be ejected. 



The cardiac glands (Plate LXIV, figs. 1 "and 7, s.l. g.) lie on either 

 side of the anterior end of the stomach, and are separated from one 

 another by the oesophagus. They are round or oval in shape, and are 

 attached to the wall of the gut by fibrous bands. In structure they 

 resemble the pair just described. A fine duct emerges from the anterior 

 end, and passes forwards to the head. Landois states that it enters the 

 ' crop ' (pharynx) but the present writers have not succeeded either in 

 tracing the duct into the head or in finding any channel entering the 

 crop except the oesophagus. 



