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J. BRONTE GATENBY. 
ectoderm. These cells only differ from the other somatic 
cells in that they are more elongate, their nuclei and cyto- 
plasmic structure being normal. 
It is a curious fact that Silvestri, though not paying much 
attention to the formation of the germ layers, has not figured 
the invagination of the endoderm (PI. 11, figs. 14 and 19). 
I cannot but believe that this happens in Oophthora, where all 
our other stages are almost identical. 
In Oophthora that remarkable nuclear arrangement of 
early stages (PI. 11, figs. 16 and 21) has not been described, 
and it possibly is absent ; however, Prof. Silvestri does not 
appear to have paid great attention to the nuclei of early 
stages, and it may have been overlooked. I mention this 
because the early changes in the nuclei of Trichogramma are 
so striking. 
As Silvestri has pointed out, Encyrtus aphidivorus is 
not a parasite on aphids, but a hyperparasite on one or two 
other true aphid parasites. With regard to the fate of the 
embryonic membrane which he figures enveloping the larva 
(on p. 69, fig. xxix) he says: “E in tale stato di sviluppo 
che la larva allungandosi rompe nella parte anteriore e nella 
posterior e la serosa e libera comincia a nutrirsi dei tessuti 
dell’ ospitatore.” 
It will be seen that, with the exception of those parts of 
organogeny which Silvestri has not treated at length, his 
admirable work agrees fairly well with the few remarks I 
have been able to pass on the embryology of Trichogramma, 
and I have no doubt that when the Professor examines his 
stages in greater detail, his results will fall into line with 
my own. 
Summary. 
(1) Trichogramma evanesce ns lays its eggs on the 
egg mass of a beetle, Donacia simplex, a single parasite 
emerging from one host’s egg. 
(2) The ovum has a large germ cell determinant at its 
posterior pole, and in segmentation the determinant is 
