26o GLOSSINA PALPALIS [CH. 



The salivary glands (Fig. 66, Gl.S.) commence as two long 

 coiled tubes, occupying a superficial dorsal position in the abdo- 

 men, on each side of the heart. The coils of the glands may ex- 

 tend as far backwards as the fourth or fifth abdominal segment. 

 After many twists and turns each tube runs forward to the waist 

 and after passing into the thorax diminishes rapidly in diameter, 

 becomes more or less straight, and at the same time passes to 

 the ventral side of the body. From this point the salivary 

 gland becomes the salivary duct. In the thorax the ducts 

 run on each side of the duct of the crop and passing under the 

 proventriculus, reach the neck, where they become so extremely 

 attenuated that their course is difficult to follow. As they 

 enter the neck the ducts curve over towards each other and 

 pass under the brain and then under the pharynx, uniting in 

 a median duct shortly before opening in the hypopharynx. 



The crop, or sucking stomach (Fig. 66, /.), is morphologically 

 a ventral diverticulum of the hinder end of the oesophagus, 

 arising from the point at which the latter communicates with 

 the proventriculus, in such a way as to appear as a direct 

 continuation of the oesophagus. It consists of a slender tube or 

 duct running backwards below the first part of the intestine 

 and expanding distally into a large sac, occupying the first 

 two abdominal segments. Usually the crop is filled with gas 

 but shortly after feeding it is found filled with blood. 



The Malpighian tubules arise by a pair of main stems given 

 off from opposite sides of the tenth limb of the intestine. Each 

 of these stems soon divides into two, and the four tubules 

 thus formed ramify throughout the body of the insect. 



Bionomics. Glossina palpalis is only to be found at the 

 edge of water, or water courses. It especially frequents the 

 banks of rivers and lakes that are surrounded by overhanging 

 trees, or scrub, but occasionally it occurs in regions where there 

 is practically no shade, as for example, on Lake Tanganyika, 

 where the shore is bare but for the presence of a few reeds. 

 In the Congo the fly frequents those parts of the rivers that are 

 surrounded by dense forest and, accordmg to Roubaud, this 



locality is determined by the necessity of two conditions 



a high and constant temperature, and an almost saturated 



