DEVELOPMENT OE THE OVARIES IN THE BLOWFLY. 
429 
nated eggs whilst they still lie in the ovary ; this layer was 
described hy Weismann, and called by him the Blastoderm ‘plasma 
(Keimhautblastevi) . He supposed that it is this layer which 
forms the blastoderm. In my sections it projects in places as 
if it possessed the power of amoeboid movement, more especially 
at the anterior egg-pole * (fig. 10, a ) ; these may, however, he the 
result of post-mortem contraction. The central granular yelk- 
substance consists of small granules, 2 to 3 p in diameter 
(fig. 11), imbedded in an apparently structureless, possibly in the 
living egg semifluid, matrix. These granules are spheroidal, 
stain deeply, and exhibit either a dark or light centre with 
alterations of the focus of the microscope. In the ripe 
unimpregnated ovum I have entirely failed to find any nuclei or 
cellular elements of any kind, and I feel sure that if any such 
elements were present they would be readily distinguished in my 
sections. 
It is not necessary for my purpose to enter into any details in 
regard to the structure of the chorion and the nature of the 
vitelline membrane; there are, however, some controverted points 
upon which I would say a few words. 
It is generally held that the epithelium of the egg forms the 
chorion as an exudation from its inner surface (E. Korschelt, 14 ; 
Weismann, 26). Whether this is so or whether the chorion is 
formed from the cells themselves (Leuckart, 16), the manner in 
which the ova leave the oviducts is entirely in favour of the 
latter view. This is effected by the rupture of the remaining 
rudiment of the egg-string between the ripe egg and the imper- 
fect ovum immediately in front of it. Thus the thin tunica 
propria and the epithelium of the egg descend in the ovarian 
follicle and enter the oviduct together. The remains of the egg- 
string attached to the unripe ovum in the ovarian follicle have 
been seen and described by several observers, notably by 
Miiller, Landois (15), and Leuckart (16). I hold therefore that 
whether the cellular epithelium is shed with the thin cuticular 
egg-sheath in the oviduct, or whether it remains as the chorion 
* The polar globules of Robin, which he described as formed by budding 
and fission, are possibly only mobile processes of this layer in a contracting 
yelk. 
32 * 
