702 THE GENERATIVE ORGANS. 
which has been very generally adopted in text-books and widely 
accepted, is that the egg-cell only is enclosed in the chorion, 
and that the nutrient cells remain outside the primitive chorion 
in contact with the micropyle, and ultimately disappear or are 
absorbed in the nutrition of the egg-cell. 
This view is very tempting on theoretical grounds ; and if it 
were true many difficulties in the interpretation of the nature 
of the Merdistic ova of Insects would disappear. The Merdistic 
and Pandistic ova would then only differ in the manner in which 
the egg-cell is nourished, and the yelks would represent single 
cells, the nuclei of which might be regarded as germinal vesicles. 
A careful examination of the ova in all stages of development 
has, however, convinced me that there are no grounds in the 
Blow-fly at least for Brandt’s view. Weismann [2] states dis- 
tinctly that the nutrient cells are enclosed within the chorion 
with the egg-cell, and that they all take part in the formation 
of the yelk by fusing into a single mass. 
It is a fact of great significance in this relation that the 
nutrient cells do not shrivel and disappear, but they increase in 
size like the egg-cell, only more slowly, and they continue to 
increase in size after the egg-cell is entirely converted into yelk 
and in turn become converted into yelk themselves. 
Numerous drawings have been published, notably by 
Korschelt [849, Fig. 49], and Henking [850], in which the 
chorion is represented between a group of cells and the mature, 
or nearly mature, ovum. These puzzled me for a long time, 
until I discovered a similar appearance in one of my own 
sections. Since then I have several times seen the same 
thing, and it is clearly due to the displacement of an immature 
ovum, which, being soft, has formed a kind of cap over the 
anterior end of a mature ovum behind it. 
The so-called alternating yelk bodies and germ ova, which 
are seen so frequently in the ovarian tubules of many insects 
in which numerous ova are developed in each tubule, are more 
difficult to explain ; but it appears to me probable that in such 
cases several series of ova are developing at the same time ; 
and that the group of cells described as intervening between 
