500 Royal Society . — 



ment of insect eggs generally, that I withheld my notes from pnbli- 

 cation, in order to add to them some account of the process of true 

 egg-formation in the Insecta, which would enable me to point out 

 more satisfactorily the differences between, or the identity of, these 

 two processes. 



In all female insects there are two ovaries, each consisting of at 

 least two egg-tubes opening into a common chamber, the uterus. 

 The egg originates and attains to nearly its full size in the egg-tube, 

 and it is therefore with this portion of the generative organs that 

 we are now mainly concerned. 



The egg-tubes differ very much in number and length. In all the 

 larger orders, except perhaps the Lepidoptera and Ileteroptera, some 

 species have very few, while others possess a great many. Thus in 

 Coleoptera, Lytta vesicatoria has a great many, Lixus has only two ; 

 in Orthoptera, Acheta domestica has a great many, while in a small 

 Locusta I only found six ; in Neuroptera, Libellula has a great many, 

 Psocus only five ; of the Diptera, the majority have many, Melo- 

 phagus only two ; in Homoptera, Coccus has a great many, while 

 Aphis Padi has only three ; in Hymenoptera, Jpis mellijlca has about 

 1 70, and Chelonus has only two ; and even in so small a group as the 

 Dermaptera, Labidura gigantea has, according to Leon Dufour, only 

 five, while Forficula auricularia has a great number. 



The number of egg-germs in each egg-tube differs also very much. 

 The Lepidoptera, in which the number of egg-tubes is very small, 

 have a great immber of egg-germs in each, while the Homoptera, in 

 which the egg-tubes are so numerous, have very few egg-germs in 

 each tube. On the other hand, in Heteroptera, the number varies 

 very little ; while in Coleoptera, Hymenoptera, and Diptera, it differs 

 greatly, though not so much as that of the egg-tubes. The number 

 of egg-germs is, however, by no means so easy to determine as that 

 of the egg-tubes. It is probable that in each species the number 

 is definite, except perhaps where it is very numerous, as, for instance, 

 in certain Lepidoptera which have more than a hundred. In most 

 egg-tubes, however, the egg-germs become so " small by degrees,'* 

 that it is almost impossible to say exactly how many there are. 



Each egg-tube consists generally, if not always, of two membranes. 

 The outer or muscular one is very evident in Hymenoptera, Geode- 

 phaga, Diptera, and indeed in most insects, but in some cases I could 

 not distinguish it. The inner membrane is delicate and structureless. 

 On its inner side lies a layer of epithelial cells, which in most parts 

 form a continuous layer ; but in those insects which have a group of 

 vitelligenous cells between each of the egg-germs, they are at these 

 parts more sparingly distributed. 



These epithelial cells probably take an active part in the secretion 

 of the yolk in all insects, and are the principal, if not the only organs 

 which form the yolk in Orthoptera, Pulex, and the Libellulina. 



Between each of the egg-germs in Lepidoptera, Diptera, Hyme- 

 noptera, Geodephaga, Hydradephaga, and Neuroptera (except the 

 Libellulina), is situated a group of large cells. These were first 

 noticed by Herold, who described them as rings ; Stein, however. 



