GLOSSINA: REPRODUCTIVE ORGANS 143 



upon the age of the fly and stage of the reproductive process. In 

 young females which have not yet begun gestation the diameter of 

 the principal branches is twice that in the gravid females, but the 

 ramifications are much less numerous, and each gland is limited to 

 a small white tuft at each side of the uterus. 



In females in an advanced stage of gestation these glands are seen 

 to have taken on an excessive increase. On the dorsal surface there are 

 four principal branches which arise from a common longitudinal trunk 

 and pass over all the length of the growing larva. The lateral 

 branches, passing round the sides and towards the ventral surface, divide 

 up into innumerable ramifications, which, anastomosing with one 

 another, produce a rich network of glandular tubes throughout the 

 abdomen ; the ultimate terminations end blindly. They penetrate into 

 the interstices of the fat body, but there is no continuity between the 

 two. The cellular walls are simply in intimate contact. 



The epithelium of which these glands are composed presents different 

 appearances in the different regions. In the proximal part of the organ, 

 a little in advance of the union of the two principal trunks to form 

 a common canal, the secretory cells are cubical, highly vacuolated on 

 their internal aspect, and enclose a lumen which is circular on section 

 and relatively large. Internally there is a fine layer of chitin, from 

 which a series of spine-like projections pass into the lumen. The nuclei 

 are small and spherical, the chromatin network indistinct, and there is a 

 large centrally placed acidophile nucleus. In sections through the young 

 ramifications, on the other hand, the secreting cells are higher, and 

 the lumen correspondingly reduced. The cells are only a little vacu- 

 olized, the chromatin network is distinct, and the nucleus usually 

 eccentric. There is no trace of the chitinous lamina internally. 



Sections through the common duct show that it is in reality com- 

 posed of two ducts which are united in a common muscular investment. 

 The epithelium is replaced by a layer of small hypodermal cells, and the 

 internal chitinous lamina is much increased, and presents an arrangement 

 similar to that of the ducts of the spermathecae. The glands open on a 

 small conical papilla which may be regarded as a sort of teat, since it is 

 directed towards the mouth of the larva. 



The cytoplasm of the cells of these glands has a remarkable affinity 

 for stains, which makes the finer details of the histology difficult to 

 follow. It is easily stained in the fresh state by neutral red, methylene 

 blue, etc. 



The fluid secreted by these glands is of a milk white colour when 



