168 Dr. R. Leuckart on the Asexual Reproduction 
body in their interior in aceordance with the type of egg-forima- 
tion. 
It is certainly the best proof of the correctness of this view, 
that by the investigation of the later stages of development we 
attain directly to the conviction that the embryo is produced 
from that part of the germ-chamber which we have just referred 
to as the reproductive body on account of its morphological re- 
lations. And this conviction must force itself upon every one 
who has even once had an opportunity of observing the pro- 
cesses of embryonic development in these animals. 
According to my observations, these processes commence in 
germ-chambers of about 0°12 millim. in length and 0-05 millim. 
in breadth, by the surface of the granular ball becoming sur- 
rounded by a germinal membrane, exactly in the same way as in 
the fecundated ovum (figs. 9 & 10)*. 
The granular mass, or yelk, as we may therefore cal it with 
perfect justice, has by this time filled up about two-thirds of the 
germ-chamber, and inflated this in such a manner that the 
former pointed pole which contains the yelk-mass has now be- 
come the thickest. The opposite or anterior end is filled with 
the formative cells of the vitellus, which, as before, persist im 
their entire quantity, but have lost their former protoplasm almost 
entirely, and are consequently reduced essentially to the clear 
nuclei (between 0:01 and 0-019 millim. in diameter), all of 
which now show a large but not very distinet nucleolus (fig. 9). 
From analogy with the formation of the ovum, we might 
perhaps have expected that the embryonic development would 
only begin when the vitelline mass had overgrown the entire 
germ-chamber and the formative cells of the vitellus had dis- 
appeared, with the exception of a small residue (Stein’s corpus 
luteum). But our germs comport themselves so far differently, 
that, even before the conelusion of their individual develop- 
ment, they commence the discrimination of the embryo, exactly 
as is the case with the so-called germ-grains of the Aphides. 
There is also another agreement between these two asexual re- 
productive bodies—the so-called chorion never being formed in 
either of them, so that the vitellus remains without that enve- 
lope which has so remarkable and peculiar a development in the 
true eggs of Insects. 
* See Weismann, /.c. taf. xii. fig. 2. (The analogy here indicated is also 
probably referred to in the assertion made by the reporter to the St. Peters- 
burgh Academy, K. E. von Baer, in opposition to Wagner’s supposition that 
the germs of the Cecidomyi@ originate from the fatty body,—namely, “I 
should rather give the name of yelk-masses to the masses from which the 
daughter larvee are developed. They closely resemble the yelk-masses of 
other Diptera, especially those of Chironomus as described by Dr. Weis- 
mann.”’) 
