PLANOCERA ELLIPTICA. 
9 
I. 
THE EGG BEFORE IT IS LAID. 
I have seen the egg when it was but a simple cell, which the most practiced eye 
could not have distinguished from the constituent cells of the organic tissues, had its 
situation and its further development not been a subsequent warrant of its true nature. 
This first observation was made in the fall of 1848. The eggs, at that season, were 
undoubtedly primordial cells, formed according to the process to which I have called 
attention elsewhere.* These cells now, were to take a predetermined development, 
a given direction ; in other words, lead a life independent of the life of the maternal 
body, endowed with a circle of activity of their own. From that time they become 
the initial centre of as many individuals, although still connected with the original 
matrix. 
Indeed, during the ensuing winter, these primordial cells had already acquired 
such a development, that any one, familiar with the subject, could recognize an egg 
at the very first glance. Their size was considerably increased, and the germinative 
vesicle and germinative spot, being now present, there was no possibility of being 
misled in regard to them, even if the eggs, compared with the size of the organic 
cells, had not answered all objections. 
Besides the germinative vesicle and the germinative spot, the nature of the con- 
tents already showed the egg : a vitellus or yolk, composed of small nucleated and 
homogeneous cells. These vitelline cells filling the whole of the yolk’s sphere with- 
out any tendency of being more particularly crowded around the germinative vesicle 
(fig. 1 — 4). The vitellus itself was semi-transparent, owing to the small amount of its 
substance, then in process of formation. 
The germinative vesicle is proportionally large and the germinative spot small, 
compared to the egg itself. The microscopic powers, then at my command, 
could not reach the structure of their contents. 
A few weeks before they are laid, the eggs appeared as represented in figs. 5 and 
6 : nearly full grown. The mass of the yolk has increased so as to render the sphere 
entirely opaque (fig. 5). A transparent area, however, is seen upon one point where 
the germinative vesicle approximates to the surface of the sphere (fig. 6). At this 
stage of development, the germinative spot could no longer be perceived. The out- 
line of the germinative vesicle itself became vague as if on the eve of disappearing 
also. It, however, does not disappear entirely before the eggs are deposited. 
* Amer, Jour, of Sc. and Arts, 2d series, vol. ix. 1850. 
