64 Dr. Burnett on the Development of Viviparous Aphides. 
A few days after the appearance of these insects, the individu- 
als of second brood (B), still, within their parents (A), had reach- 
ed two-thirds of their mature size. At this time the arches 0 
the segments of the embryo had begun to close on the back, and 
the various external appendages of the insect to appear promi- 
nently; the alimentary canal ‘had been more or less completely 
formed, although distinct abdominal organs of any kind belonging 
to the digestive system were not very prominent. At this period, 
and while the individuals of generation B, are not only in the 
abdomen of their parent A, but are also enclosed, each, in its 
primitive egg-like capsule,—at this time, I repeat, appear the first 
traces of the germs of the third brood (C). 
These first traces consist of small egg-like bodies arranged, two, 
three, or four in a row, and attached in the abdomen at the locality 
where the ovaries are situated in the oviparous forms of these al- 
imals. 
These egg-like bodies consisted either of single nucleated cells, 
of 5;'55 of an inch in diameter, or, a small number of such cells 
enclosed in asimple sac. These are the germs of the third gene- 
ration; they increase with the development of the embryo in which 
they have been formed, and this increase of size takes place 
not by a segmentation of the primitive cells, but by the endog- 
enous formation of new cells. After this increase has gone on 
the sac by which it is enclosed. In this way the germs are mul- 
tiplied to a considerable number, the nutritive material for theit 
growth being apparently a fatty liquid with which they are bathed, 
contained in the abdomen, and which is thence derived from the 
abdomen of the first parent. 
When these germs have reached the size of =}, of an inch in 
diameter, there appears on each, near one end, a yellowish, vitel- 
lus-looking mass or spot, which is composed of large, yellowish 
ells, which in size and general aspect, are different from those 
constituting the germ proper, This yellow mass increases part 
passu with the germ, and at last lies like a cloud over and con- 
cealing one of its poles. I would also insist on the point that it 
: 
meaner 
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