256 PROCEEDINGS : BOSTON SOCIETY NATURAL HISTORY. 
beneath these dorsal ectodermic thickenings, but is not formed at 
the same time at the two poles of the egg. At the anterior end it 
extends dorsally more rapidly than at the posterior portions (Fig. 9). 
I found no trace of the lateral gastrular invaginations which Graber 
(’ 89 ) describes in Callipliora as accompanying the median invagi¬ 
nation, and which, as Korschelt and Ileider (’ 92 , p. 812) have 
remarked, undoubtedly mark the edges of the germinal plate. 
The germinal plate, as in other Diptera, is superficial in position 
and unprotected by embryonic envelopes, the amnion being repre¬ 
sented by only the merest rudiments at the anterior and posterior 
extremities of the germinal plate (PI. 2, Fig. 9, am .), on the dorsal 
surface of the egg. These rudiments mark the limits of the head¬ 
fold and the tail-fold, the former being the dorsal portion of the 
germinal plate at the anterior end of the egg {pli. ce.), and the latter 
the dorsal portion of the germinal j)late at the posterior end of the 
egg {pli. ca.) . Even these rudiments of an amnion disappear in the 
stages immediately following. 
Figure 9 represents a sagittal section of an embryo somewhat 
older than that shown in Figure 8. The anterior end of the egg 
is marked by the presence of the micropyle ( mr’py .). The head¬ 
fold {pli. ce.) extends as far as the anterior amniotic rudiment and 
contains mesoderm, whereas the tail-fold {pli. ca .), which extends 
to the posterior amniotic rudiment, consists as yet exclusively of a 
thickened ectodermic plate. 
The proctodeum and stomodeum both make their appearance as 
ectodermal depressions on the dorsal portion of the germinal plate. 
In common with Musca, as observed by Graber (’ 89 ) and Voeltzkow 
(’ 89 ) , the proctodeum appears first. Figure 10 (PI. 2 ) represents 
a sagittal section of an embryo somewhat older than the one previ¬ 
ously mentioned; in it the proctodeum has the form of a deep 
invagination in the tail-fold, while the stomodeum has not yet 
appeared. The point in the head-fold where the stomodeal invagi¬ 
nation will appear is, however, plainly shown in the thickening near 
the end of the fold {eras. stmd.). It will also be noticed in this 
embryo that the primitive mesoderm has extended beneath the 
tail-fold, that the posterior amniotic rudiment has disappeared, and 
that the germinal plate has begun to show traces of segmentation. 
Tracheal invaginations have not yet made their appearance. 
Figure 12 (PI. 2) shows a stage still older than the one just 
discussed, in which both proctodeum and stomodeum'are present. 
