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32 flies not reproducing, or doing so only feebly. But this was not the case: though they were all smaller than ordinary flies—many of them indeed being strikingly small, having doubtless absorbed less food than the normally fed larvae,—yet on the 6th of June, the same day on which the flies derived from the latter began laying eggs, they too laid abundantly for the first time. And the matter did not stop here, for the process was often repeated subsequently. In order to be sure, however, that even the smallest of them,—that is, those which had been most affected by the bad feeding—were reproducing, I isolated five of the smallest flies. After seven days they had produced two large packets of eggs; and this process was repeated four times within the next fortnight.

There could therefore be no doubt that, in spite of the scanty supplies of food during larval life, the organs of reproduction, or at any rate their essential part—the ovaries, were normally constituted; so that with good nutrition during the imago-stage these flies reproduced in a perfectly normal manner.

I was however able to prove that the external reproductive parts were also normally developed. A number of females were isolated in small cages immediately after their escape from the pupa and abundantly fed. These too in course of time laid eggs, not a single one of which developed into a larva. It therefore follows that the eggs, of Musca vomitoria lack the capacity of developing parthenogenetically; and hence all the eggs of the ill-fed flies were fertilized. This however would only have been possible if the entire