ON THE EOEMATION OF THE EOO IN THE ANNHLOSA. 
699 
would appear that in insects, as the Purkinjean vesicle surrounds itself with a well- 
defined portion of yelk, the original vitelligenous nucleus also forms a pseudo-cell ; so 
that the vitelligenous body of Glomeris^ which corresponds with the Purkinjean vesicle, 
is also homologous with the nucleus of the vitelligenous pseudo-cell of insects. 
The action of tartaric acid is much like that of acetic acid. Ammonia renders the 
macula invisible, and the Purkinjean vesicle almost invisible, but it does not make the 
yelk-matter dark. Water does not act energetically on these tissues. 
WTien the egg-germ has attained a length of about of inch, the vitel- 
ligenous bodies have gradually disappeared, and the yelk-substance begins to present, 
under transmitted light, a dark colour, like that which at an earlier stage it assumes 
under the action of acetic acid. The Purkinjean vesicle can still be seen indi- 
stinctly; but when the follicle has attained to a length of ^th of an inch it has 
become quite opake, and the Purkinjean vesicle can only be seen after the application 
of pressure. 
Up to this time, however, the yelk is suiTOunded by no vitelline membrane, and 
indeed the majority of the oil-globules seem to be produced in the stroma, and not in 
the egg-follicle itself. The yelk consists of a clear fluid, containing an immense quantity 
of small oil-globules, varying up to inch, of which size there are a great 
number. 
The largest follicles were about of an inch in length, and contained eggs 
which were already surrounded by a firm chorion. On carefully tearing this open, the 
Purkinjean vesicle could generally be perceived. It was from to of an 
inch in diameter, spherical and transparent, but the wall was often, as it were, stained in 
places. When seen sideways this gave the effect of a patch, as in fig. 3 ; but when looked 
at from in front it could only be seen faintly, and had, under a high power, no definite 
outline. 
The macula at this stage consisted generally, if not always, of two vesicles, one of 
them more than twice as large as the other. The latter, which is no doubt derived 
from the large one, first appears when the Purkinjean vesicle is about aoVo ths of an 
inch in diameter. Under the action of acetic acid it disappears, as does the large 
macula ; and its occurrence is very constant, since I found it in every Purkinjean vesicle 
which was more than x poo ths of an inch in diameter. 
I did not find any mature eggs until the beginning of September ; and even at this 
time many females did not contain any ; and in all there were only a few eggs which 
had escaped from their capsules. These lay free in the cavity of the ovary or ovi- 
duct; they had a leathery chorion, and, like the eggs of insects, seemed to possess 
no second envelope. They are about ^th of an inch in size, and of a broad elliptic 
shape. 
I could find in them no trace of the Purkinjean vesicle, nor of the maculae. The 
yelk consisted, 1st, of an apparently viscid substance ; 2ndly, of minute molecules ; and 
3rdly, of oil-globules from To o o o th to xoooofhs of an inch in diameter. If they were 
