469 



and extends backwards to a point one-quarter the length of 

 the abdomen from the posterior extermity of the insect. 

 Its cells are large, and continue to develop a lumen, which 

 runs right down the gland, but increases slightly in diameter. 

 The cells soon lose their embryonic appearance; in the pupa 

 at the end of its first day they are already wedge-shaped; 

 they have a large nucleus but present a fairly clear cytoplasm. 

 In the thirty-six hour pupa, however, some of them show 

 a distinct indication of developing granular cytoplasm. The 

 granulations increase in number, so that in the mature pupa 

 the whole cells become packed with granules; the glandular 

 nature of the organ is no longer to be questioned (figs. 182, 

 183). 



The gland on the left side develops into a structure 

 only two-thirds the length of its fellow. Distally its lumen 

 is distended into a round vesicle, and this becomes connected 

 on its anterior side with a round, solid ball of cells, the spaces 

 between which appear to open into the vesicle (figs. 180, 181). 



The function of these glands is doubtful. That they are 

 not ''colleterial glands" (glue-secreting glands) seems certain, 

 for the wasp has no need to fasten her egg to an exposed sur- 

 face. It is much more probable that they are lubricating 

 glands, whose secretion aids that of the true lubricating glands 

 in facilitating the passage of eggs down the ovipositor, and 

 the 'entrance of the ovipositor through the hard shell of the fly 

 pupa during oviposition. 



To somewhat similar glands in CalUphora, Lowne has 

 applied the term ''Parovaria." As late as 1895 he main- 

 tained, in his well^-known monograph on that insect, that the 

 germinal material of the egg was developed in the parovaria, 

 while the yolk was produced in a pair of great ''yolk glands" 

 (really the ovaries), and that the large oval masses of yolk, 

 as they pasesd down the uterus, first applied their microphyles 

 to the opening of one of the parovaria, and received their 

 germinal vesicle ; then applied their micropyles to the openings 

 of the spermathecae, and were fertilised. Lowne then drew 

 the unfortunate comparison of the "insect vitellogen" with 

 that of the flat worms. 



It is necessary to consider now the history of the oogonia, 

 in their process of development into ova. 



Throughout larval, and the greater part of pupal life, 

 the oogonia reinain as small cells closely packed together, 

 measuring from 5f/x to 6^jut in diameter; each contains a large 

 nucleus of the "vesicular" type, i.e., the chromatic material 

 ,is contained in a minute granule, lying within a colourless 

 nuclear "sap." But towards the end of pupal life these cells 



