154 



The Reproductive System. — Each ovary con- 

 sists of a large number of follicular tubes whose 

 lower ends open into the ovarian tube, and 

 whose upper ends terminate in a delicate sup- 

 porting filament (terminal filament). The apex 

 of the ovary is formed of a single follicular tube, 

 whose filament is attached to the fat-body of the 

 fourth segment. 



Around the whole ovary there is a delicate 

 nucleated sheath. 



Each follicular tube contains one or more 

 egg-follicles in different stages of development. 

 In the freshly-hatched mosquito each follicular 

 tube contains an undeveloped egg-follicle. As 

 this develops, a second and a third undeveloped 

 follicle appear above it, which again undergo 

 development into mature eggs. The follicle at 

 first consists of two to four large cells, with large 

 nuclei surrounded by a single layer of smaller 

 epithelial cells (Fig. 39). 



The central cells then increase in size and 

 number, so that many very large cells are con- 

 tained in the now enlarged follicle. The sur- 

 rounding epithelial cells also become larger, and 

 rapidly increase in number so as to form a layer 

 of regular cubical cells surrounding the follicle. 

 The central cell nearest the ovarian tube is the 

 ovum, the rest are nurse cells, and eventually dis- 

 appear. Both the ovum and the nurse cells in- 

 crease greatly in size. The nurse cells have clear 

 protoplasm and extremely large nuclei, which 

 exhibit karyokinetic figures. The ovum contains 

 very numerous yolk granules, which occupy the 

 whole of its substance, except a thin coating 

 of granular protoplasm. Still later this thin 



