36 ON THE AGAMIC REPRODUCTION AND MORPHOLOGY OF APHIS 
chamber are different from those of the upper. As much as a third 
of the whole chamber may be occupied by a mass of periplast con- 
taining only a single clear vesicle. Such a condition is figured in fig. 1, 
Pl. XXXVI. [Plate 1] fig. 2 exhibits a further advance in the same 
direction ; the mass which, from its close resemblance to a true ovum, 
I have called a pseudovum, having enlarged so much as nearly to 
equal the contents of the terminal chamber, from which it is dis- 
tinguished by a slight constriction. In figs. 3 and 4, the constriction 
has become more marked, until at length a penultimate chamber is 
formed, connected only by a narrow neck with the terminal one, fig. 4. 
It is on an average about ;3,th of an inch in diameter. The epithelial 
layer (c) of its wall is ordinarily well developed, and, when water is 
added, swells up, so as to separate the periplastic substance of the 
pseudovum from the wall. The periplast itself exhibited no structure, 
and appeared unchanged, except in size. The clear vesicle was 
sometimes unchanged, sometimes enlarged, but otherwise unaltered. 
Of its endoplast I was sometimes unable to discover any trace; on 
other occasions I found a few granules in its place (fig. 3); and, once, 
two particles, each rather more than half its diameter, appeared to lie 
side by side in the interior of the vesicle. 
The marked contrast between the perfect distinctness of the endo- 
plast in the vesicles contained in the ultimate pseudovarian chamber, 
and its apparent absence in the very similar vesicle of the mass con- 
tained in the penultimate chamber, or in the lower part of the last 
one, was the more striking, as the two could be readily compared 
under the same circumstances and in the same field of view. 
Finally, the vesicle itself ceases to be visible (fig. 4), and the 
penultimate chamber contains only its epithelium and a mass of 
apparently structureless substance ;—I say apparently structureless, 
because the addition of water made the mass more clear, and at the 
same time rendered an irregular areolation and scattered granules 
visible in its substance. Whether the areole are the outlines of 
delicate vesicles, and the granules their endoplasts, or not, are points 
which I could not satisfactorily determine ; at any rate, I could never 
observe anything like the regular structure observable in the contents 
of this chamber when a little larger. 
Fig. § represents such a chamber, ;3,;th of an inch in length. The 
endoplasts of the wall are seen lying in or upon it, and occupying its 
interior is a distinct oval mass of substance agreeing in appearance 
with the periplast of the pseudovum, but distinguished from it by 
containing a great number of clear spheroidal cavities not more 
than s255th of an inch in diameter, each of which contains a central 
