577 



perhaps hardly sufficient to enable us to generalize upon it as yet 

 with much confidence. As far, however, as we at present are aware, 

 alternate groups of large vitelligenous cells are found in all Lepi- 

 doptera, Diptera, Hymenoptera, Neuroptera (except Libellulina), 

 Geodephaga, and Hydradephaga. The large vitelligenous cells are 

 contained in a terminal chamber in other Coleoptera, Homoptera, and 

 Heteroptera; whilst apparently they are absent in Orthoptera, 

 Libellulina, and Pulex. 



This curious subdivision of the Insecta is not exactly that which 

 would be given by any other characters. It is, however, remarkable, 

 that the mode of formation of the thorax would divide the Insecta 

 into two groups very nearly equivalent to those just mentioned, 

 except as far as regards the Geodephaga and Hydradephaga. 



In fact, the Coleoptera, Orthoptera, Dermaptera, and Hemiptera 

 have a very large prothorax, while this segment is small in the Lepi- 

 doptera, Diptera, Hymenoptera, and most Neuroptera. In the 

 Libellulina, however, it is distinct from the rest of the thorax and 

 considerably developed. 



In the Orthoptera, Libellulina, and the genus Pulex, we find the 

 simplest type of egg-formation which occurs among the Insecta, the 

 large vitelligenous cells being entirely absent, and their functions 

 probably monopolized, instead of being only shared, by the layer of 

 epithelial cells. 



The macula germinativa, which is in fact the nucleus of the ger- 

 minal vesicle, has in the Orthoptera, as usual, the form of a small 

 round vesicle. 



In (Estrus the germinal vesicle contains several small vesicles, one 

 of which grows much larger than the remainder, and becomes the 

 macula germinativa. 



In Pulex the germinal vesicle is dark, and the macula germinativa, 

 which is very distinct in the young egg-germs, soon disappears. 



In the Coleoptera (except the Geodephaga and Hydradephaga), 

 the Homoptera, and the Hemiptera, each egg-tube ends in a large 

 terminal chamber, full of round cells, each of which can apparently 

 become either an egg-cell or a vitelligenous cell. 



In Nepa and some other forms, I found, as Prof. Huxley first 

 discovered in Aphis, a duct or passage leading down from the ter- 

 minal chamber to the egg-germs. In one specimen there were four 



