579 



wards the type which prevails in the Lepidoptera, Hymenoptera, and 

 Diptera. 



In these four orders, and in the Geodephaga and Hydradephaga, 

 each egg -chamber contains, at its upper end, a group of large vitelli- 

 genous cells, which are generally few in number in the Neuroptera, 

 rather more numerous in the Diptera, and still more so in the Geode- 

 phaga, Hydradephaga, and Hymenoptera. 



In all these six groups, except the Diptera, each egg-chamber is 

 divided into two parts by a transverse constriction, which separates 

 the vitelligenous cells from the germinal vesicle and the yolk sur- 

 rounding it. At first, the lower division of the egg-chamber is quite 

 small, but it grows gradually larger at the expense of the upper 

 part. 



In the Diptera the egg-chamber is not divided into two smaller 

 chambers, but has a rounded or oval form, and contains a number of 

 vitelligenous cells, the lowest of which becomes darker from the 

 formation of granular yolk-matter, and thus forms the egg-cell. Its 

 nucleus becomes the germinal vesicle. The wall of the egg-cell 

 gradually disappears, and the yolk -mass being enlarged by the yolk 

 secreted by the vitelligenous cells, continues to increase until it 

 occupies the whole egg-chamber. 



Between each egg-germ, in the Diptera, the egg-tube becomes 

 extremely narrow, which is not so much the case in other Insecta. 

 It is remarkable, that Pulex, which is in many respects nearly allied 

 to the Diptera, should differ from them so greatly in the mode of egg- 

 formation. 



The germinal vesicle in the Carabidse generally contains, besides 

 the macula germinativa, several small vesicles, which indeed are 

 sometimes very numerous. In Carabus violaceus, the macula itself 

 appeared to consist of many small oval masses, and in one specimen 

 the macula appeared to have broken up, and the constituent bodies 

 were floating about loose in the germinal vesicle. From these 

 observations, and from what has been mentioned as occurring in 

 Pulex, I am disposed to think that the first embryonic cells, at least 

 in Insecta, appear in this manner. 



According to M. Leon Dufour, Chelonus oculator, one of the small 

 Ichnenmonidae, possesses no ovary nor eggs, but merely four long 

 tubes leading into as many matrices, containing a great number of 



VOL. ix. 2 R 



