364 ME. LUBBOCK ON THE OVA AND PSEUDOTA OF INSECTS. 
water or in the open air, and this may perhaps account for the small size of the coUeterial 
glands. 
At this period the egg-contents consist of yellowish oil-globules, colourless yelk-cells, 
a small quantity of fluid, the green globules which give the egg its colour, and the 
parasitic, oval green cells, which are congregated near the cephalic end. 
Dr. Leydig describes the first trace of the embryo as arising at the free end of the egg, 
and then extending with a waved course as a clear streak across the egg. It seems to 
me, however, that the first trace of embryo is at the basal end of the egg, and I think 
that he has been led into error by supposing that this embryonic structure arises imme- 
diately from the division of the vitelligenous cells (e), which we have already seen is not 
the case. Professor Leuckaet also asserts that the thickening of the blastoderm com- 
mences at the hinder pole*. 
The remainder of the egg consists, as before, of oil-globules, yelk-globules, and 
green globules, which latter, however, are more numerous round the embryo than 
elsewhere. 
Gradually, however, the yelk-cells become smaller, tolerably equal in size; and as the 
embryo continues to enlarge, they diminish greatly, being no doubt changed in some 
manner into the nucleated cellular tissue of which it consists. At the time when the 
antennffi make their appearance the yelk-cells have almost enthely disappeared. 
At this period the tissue of the embryo consists of minute cells about ^o^oo 
meter, and each containing a bright central spot. When pressed out into water the) 
often lose their distinctness, and sometimes they seem to change into green bodies, 
apparently somewhat cubic in shape, and separated a little from one another b) a 
colourless, structureless substance. What conditions are necessary to this change I was 
unable to determine. 
The small cells constituting the embryo at a very early period, when subjected to a 
weak solution of either tartaric or oxalic acid, took a variety of forms, more or less oval, 
and pointed at the narrow end. Their contents became granular. Acetic acid made the 
cell-wall less distinct and the contents opake, as if coagulated. 
Thus we see that the different bodies, which are either contained in the egg, or have 
contributed to its formation, are by no means few in number. We have, fu'st, the structure- 
less external membrane of the egg-follicle ; secondly, the cells forming the epithelium ; 
thirdly, their nuclei ; fourthly, the vitelligenous cells ; then the germinal vesicle with its 
nucleus, the oil-globules, the periplast, in which the three last substances are contained, 
the yelk-cells, the parasitic vegetable cells, the green globules, the blastodermic cells 
and their nuclei, and, finally, the vitelline membrane. 
Up to this period, and indeed until the different appendages of the embryo have 
become quite distinct, the egg has not altered its position, but still remains in the 
follicle in which it was formed ; and its head, as usual in insects, is ahvays fuidhest from 
the vulva, or rather is at the free end of the follicle. 
* FortpAanzung und Entwickelung der Pupiparen. Halle, 1858, p. 69. 
