II
figure 1). Another variety consists of a delicate oval homogeneous plasma of a
faint greenish colour, about 8 μ Χ 6 μ in size and containing about 20 granules of
pigment variously arranged (Plate I, figure 2). In a third variety we have the
cluster of pigment, within either a visible or an invisible plasma, and interspersed
with some distinct vacuoles, and also some rather refractive granules, both oí
about 1 μ or 2 μ in diameter (Plate I, figure 3). In a fourth variety, somewhat
larger in size, there are the pigment, the vacuoles and the granules, all enclosed
within a very distinct oval outline (Plate I, figure 4).
These varieties have three things in common, their pigment, their oval
shape and, approximately, their size, Often all the pigmented cells in one
mosquito belong to the same variety and are nearly of the same size. Owing
to the ambiguity in the time of feeding referred to above, it is difficult to pro-
nounce as yet upon the question as to which of the forms is most elementary ;
but I think that the order of the varieties as just given is also the order of
development. Thus the youngest cells would belong to varieties 1 and 2 ; later
the vacuoles and granules appear ; and lastly we have the definitive outline.
By degrees, towards the end of the second day, the earlier varieties disappear
and the fourth form only is found, to remain as the type for some days (Plates II
and III).
In some mosquitos of this day several varieties of the young cells are found
together, and there is considerable variation in size. Such insects, I fancy,
must have fed themselves on several occasions during the night.
The pigment consists of about 20 granules which have almost exactly the
appearance of the pigment of proteosoma. The granules may perhaps be
blacker and smaller and do not tend to form the little masses found in proteo-
soma, although they do tend to collect together in certain portions of the cell.
Very often they are subject to a rapid oscillatory motion. Their arrangement
is variable,
The vacuoles, when they appear, are very distinct and apparently full of clear
fluid, I take the present opportunity for stating that throughout this paper I
use the term "vacuole" only as a descriptive one. Their size often varies
largely even in the same cell.
The granules appear to have more substance than the vacuoles, are usually
all of much the same size, and look very like Labbe's "granules chrornatoides "
of halteridium.
The staining reactions, so far as observed, will be given in paragraph 3.
As we advance toward the evening of the second day, the cells become
larger and larger 5 the vacuoles and granules become more numerous ; the
pigment tends to collect round one, or two, or more large vacuoles ; and the
outline is more and more marked. It is proper to notice, however, that there is
a variety apparently descended from the early varieties without apparent plasma
or outline, in which the outline is finer than in the ordinary forms, while the
vacuoles and granules are much less visible. These seem to belong to the
type of the " hyaline " forms of the third and fourth days.
At the end of the second day, that is, 48 hours after feeding, the cells may,
I think, already reach a long diameter of 20 μ in a few cases,
Third Day—Tuesday.—Grey mosquitos generally lay their eggs during this
day on the surface of the water at the bottom of the test-tube, where they are
to be found as small black floating " rafts " of eggs. After this the insects
frequently die if they have not been fed again on the previous night.
In insects which have not been re-fed, we find stomach and intestine
almost free from contents and the stomach cells very clear and hyaline. The
eggs, if not laid, are fully matured.