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 obser\^ations 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. glomeraius, 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 fonned 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 

 1 1 ganglia, not including the subesophageal ganglion, ^'^' '^"^/"DtTammatic 

 is visible. The segments of the body appear to be sectional views of the pos- 

 10 in number, but subsequent development and terior end of the embryo, 



^ . showing how the hyper- 



growth in the first stage reveal 11 distinct seg- trophiedceiisof theWnd 



mentS ^^' '^^^'^^ ultimately 



■ , • , . , , 1 r ^°"^ *^^ caudal vesicle. 



The caudal vesicle, which in the larval forms is a grow out through the 

 large sac at the end of the body, is seen forming as ^°"'- ^^ shows an exter- 



. ,, . nal view of this process. 



a solid mass of long, narrow cells m the posterior a. Mass of cells; 6, anus. 

 region of the abdomen (fig. i,a). When first seen (Onginai.) 

 it lies inside the abdomen, but can be seen gradually to grow out 

 through the anal opening (fig. i, 6), 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 



