CXXlil 
either in form, size or contents from the ordinary embryonal cells. At 
one end of each gland is a short duct, which at first consists of a single 
row of embryonal cells. Subsequently the pole-cells commence 
to divide themselves anew, and thus form the vitelligenous and 
germinal vesicles, while the walls of the organ and its epithelial cells 
are composed of ordinary embryonal cells. 
It appears then, in short, from these remarkable observations, that 
the pole-cells, afler remaining for some time outside the blastoderm, 
re-enter it, collect round themselves a sufficient mass of the ordinary 
embryonal cells, and thus form the rudiments of the new generative 
organs. 
To judge from M. Mecznikow’s description and figures, very much 
the same thing appears to happen in Aphis. The cells, indeed, which 
I suppose to* be the pole-cells do not differ from the rest either in size 
or colour, and cannot therefore be traced throughout the develop- 
mental changes, as in Cecidomyia. The blastoderm, however, in their 
neighbourhood—z.e. at the hinder end of the egg—projects into the 
yolk and forms the pseudovitellus and the rudiment of the future 
generative organs, a8 was first described by Huxley in his celebrated 
memoir on this subject. We see, then, not only that the generative 
organs are present in the embryo, but even that they are the very 
Jirst organs to make their appearance. Before a single appendage is 
indicated, before the mouth or any one of the internal organs is traced 
out, the essential parts of the generative organs are already in their 
place. 
It is true that the two cases in which this remarkable fact has been 
observed are both instances of agamic reproduction. I have, however, 
shown, in my papers published in the ‘ Philosophical Transactions’ 
for 1857, 1858 and 1861, which appear to have escaped M. Meczni- 
kow's notice, that the agamic reproduction in insects closely resembles 
that by means of impregnated eggs, and I can hardly therefore suppose 
that there would be any fundamental difference in the development of 
the generative organs themselves. 
It will be observed that there is nothing in M. Mecznikow’s ob- 
servations to confirm the remarkable statements of M. Balbiani, to 
which I alluded in my last Address. It is satisfactory to know 
that this gentleman is about to publish his memoir in full, with 
figures. 
Considerations of time and space prevent me from referring to 
many other parts of M. Mecznikow’s memoir which are of great 
