DEVELOPMENT OE THE OYAETES IN THE BLOWELT. 



435 



appearances, in optical section, which could be interpreted without 

 difficulty, as Stein and Leuckart have interpreted them ; possibly 

 the fine tubes are the fine tracheae of the fat-glands, whilst the 

 cells figured by Stein are undoubtedly those of the fat-body, of 

 which I give a figure (PI. XXYIII. fig. 15) for comparison. 

 Sir John Lubbock (19), describing the corresponding glands 

 in Coccus Persicce, gives a totally different description. He 

 says : — 



" They are six in number, four large and two small, the latter 

 being apparently attached by a short stalk to the peduncle of the 

 large one which is furthest from the vulva. They lie three on 

 each side, and their ducts o-pen into the egg-canal close together 

 and about halfway between the vulva and the division of the 

 egg- canal into two oviducts. The inierual structure is very 

 distinct and interesting. It consists of many cells lying loose in 

 the internal cavity, and resembling very much in form, size, and 

 appearance the vitelligenous cells of the egg-follicle." 



I have been unable to find any other published details on the 

 structure of these glands, which I shall now give from my own 

 observations. 



The gum-glands in the Blowfly are simple tubes, tortuous 

 rather than convoluted, 2 m. in length, with an average dia- 

 meter of "175 m. They have a glistening white appearance, 

 and are beaded over the surface from the projection of the cells 

 lining them. In sections these glands are seen to consist of an 

 outer musculo-cellular coat, like the so-called peritoneal coat of 

 the oviduct. This is lined by a single layer of large epithelial 

 cells. The lumen is filled by a granular fluid or semifluid sub- 

 stance. This is coagulated by alcohol, the granules suspended 

 in it are blackened by osmic acid, and the intergranular material 

 is scarcely stained by alkaline solutions of carmine. In this 

 respect it differs entirely from the substance contained in the 

 uterine pockets and from that with which the eggs are cemented 

 together. 



The epithelial cells which surround the lumen of the gland 

 are irregular in form and measure, on an average, 80 /i in 

 diameter, and from 30 to 40 /j. in thickness. Many of these 

 cells contain very remarkable spherical corpuscles, usually 

 one in each cell (figs. 15 to 20). Besides these, some of the 



