Dec. 20, 1915 
Biology of Apanteles militaris 
497 
The mouth opens into an enlarged cavity, the pharynx, this in turn 
opening posteriorly into a very narrow esophagus, and this into the 
stomach, which is a very long, narrow, tapering tube closed posteriorly. 
There are two Malpighian vessels, which lie parallel to the stomach, 
extending anteriorly about one-half the length of the larva. 
The tracheal system has not been observed in the embryo. According 
to the observations of Weismann and Grasse, as reviewed by Korschelt 
and Heider (3, p. 334-335), the tracheal system forms early in the 
embryonic development of the Hymenoptera as compared with the 
lower forms of insects and usually contains air previous to hatching, this 
being obtained apparently from its tissues and body fluid. Seurat (7) 
states, however, from his study of A . glomeratus , that the tracheal system 
of this parasite, whose development is similar to that of A. militaris , is 
present, although he had not seen it, no doubt basing his statement on 
the fact that these organs, being ectodermal invagina¬ 
tions, are normally formed in the embryo. 
The head of the mature embryo is of one segment 
and is readily distinguished by its large size, the pres¬ 
ence of mandibles, two small tubercle-like antennae, 
and the prominent brain lobes. A nervous system of 
11 ganglia, not including the subesophageal ganglion, 
is visible. The segments of the body appear to be 
10 in number, but subsequent development and 
growth in the first stage reveal 11 distinct seg¬ 
ments. 
The caudal vesicle, which in the larval forms is a 
large sac at the end of the body, is seen forming as 
a solid mass of long, narrow cells in the posterior 
region of the abdomen (fig. i,a). When first seen 
it lies inside the abdomen, but can be seen gradually to grow out 
through the anal opening (fig. 1, b), which becomes greatly distended. 
The stomach becomes lengthened and extends outside the body into 
the vesicle, its blind end being fastened to the inside wall of the vesicle 
posteriorly and ventrally. The Malpighian tubes also extend into the 
vesicle and open through its ventral surface near the end of the 
stomach. 
HATCHING 
The embryo at the time of hatching, as previously stated, lies tightly 
inclosed in the amniotic envelope surrounded by the loose mass of serosal 
cells, the whole being surrounded by the chorion. The embryo, which 
up to this time has been curled in the egg, now straightens itself out and 
by its struggles to escape, aided by the rapid swelling of the serosal cells, 
ruptures the chorion, which has become extremely thin, owing to the 
increase in the size of the egg, and escapes into the body of its host, still 
Fig. i. —Apanteles militaris: 
A, B, C , Diagrammatic 
sectional views of thepos- 
terior end of the embryo, 
showing how the hyper¬ 
trophied cells of the hind 
gut, which ultimately 
form the caudal vesicle, 
grow out through the 
anus. D shows an exter¬ 
nal view of this process. 
a, Mass of cells; b, anus. 
(Original.) 
