502 Royal Society : — 



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

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

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

 considerably developed. 



In the Orthopterna, Libellulia, 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 CEstrus 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 

 distinct ducts, so that probably each egg- germ has a separate yolk- 

 duct. 



In Nepa there is a large lateral projection at the anterior end of 

 each egg, and it is always on the same side as the germinal vesicle ; 

 but this latter varies from side to side without any apparent regu- 

 larity. 



In the common Earwig, the egg-tubes are short and numerous ; 

 each consists of a large, lower chamber, which is more or less pear- 

 shaped, and two or three other chambers, but slightly separated from 

 one another, bent down on the lower chamber, and so short and 

 small as to resemble very closely the stalk to the pear. 



Each egg-germ in this insect consists of two parts — an egg-cell 

 containing the germinal vesicle and the yolk, and a vitelligenous 

 cell. The vitelligenous cell has no distinct nucleus, and in the 

 small stalk-hke part of the egg-tube is double the size of the egg-cell, 

 which at this period contains the germinal vesicle, but not as yet 

 any yolk-matter. In this part of the egg-tube it sometimes appeared 

 as if there were two vitelligenous cells to one egg-cell. In the large 

 lower egg-germ this is never the case. In this part of the egg-tube 

 the vitelligenous cell is still larger than the egg-cell, which however 

 grows larger, both absolutely and relatively, until it almost fills the 

 egg-chamber. 



The yolk-mass in the lower egg-germ consists of dark granules 

 and oil-globules surrounding the germinal vesicle, which generally 

 contains two or three minute cell-like vesicles. The contents of 

 the vitelligenous cell are light brown, granular, and in part arranged 



