467 



The ovaries, then, so far as external appearances are 

 concerned, reach their adult condition in the pupa of about 

 two and a half days. Terminally each consists of twelve 

 ovarian tubules, containing sexual cells, and protected by a 

 thin "capsule/' These tubules now open into a great oviduct 

 divided by a connective tissue stroma into four channels 

 for the greater part of its length; but devoid of such parti- 

 tions distally, near its opening into the vagina. The structure 

 of the mature female is shown in fig. 180. 



The further development of the contents of these tubules, 

 the oogonia, will be described below. 



It is necessary to examine now the changes undergone by 

 the vagina and its accessory glands. 



In the four-hour pupa the vagina is a small sac-like 

 invagination of the ventral body wall between the first and 

 second ovipositor appendages; its walls consist of long 

 columnar undifferentiated cells. During the next twenty-four 

 hours it grows back rapidly, and extends considerably also 

 in height, forming in the thirty-six hour pupa quite a spacious 

 chamber on the ventral body wall, close behind the beginning 

 of the ovipositor; the vagina is connected now by a distinct 

 "neck" with the exterior. Its walls are composed of cubical 

 cells; those on the upper side of the vagina, and those on the 

 anterior part of the ventral surface, develop each a sharp 

 forwardly pointing "tooth," the inner surface of the vagina 

 presenting therefore a distinctly rasp-like appearance. As 

 development proceeds the cells on the upper walls elongate 

 greatly, and adopt a columnar shape. A very delicate chitin 

 layer is formed within the vagina, and this layer presents, of 

 course, the same rasp-like appearance that occurred merely 

 as a protoplasmic mould a day earlier. The function of this 

 curious roughened surface is obviously to help in the laying of 

 eggs. The cells themselves frequently present a clear, some- 

 what vacuolated protoplasm, such as is usually seen in mucin- 

 secreting gland cells. 



On the antero-dorsal sides of the vagina a curious develop- 

 ment of the epithelium has been going on, which results 

 eventually in the formation of the lubricating glands. The epi- 

 thelium, as already stated, consists, roughly, of two layers of 

 very elongated cells ; of these cells the outer form each a gland 

 cell; the inner, the duct of the gland cell. The outer cells 

 increase considerably in size, and breaking loose from the 

 epithelium grow inwards a very short distance. They are 

 already clearly visible in the pupa of fifty-six hours, as large 

 cells with granular cytoplasm. They increase in size during 

 the pupal period, and are seen in the adult insect as a pair 

 of small groups of about thirty large cells on either side of the 



