June s, 1916 Hessian-Fly Parasites 369 



eggs of the three species studied were always found between the inner 

 surface of the puparium and the larva itself. They were transferred 

 separately, each to an unparasitized Hessian-fly larva which had been 

 previously dissected from its puparium and placed in a little glass-cell 

 cage of the following description : 



Flat glass plates i inch by 1% inches square were used, in which hollows 

 about the size and shape of a Hessian-fly puparium were ground in one 

 surface, one hollow per plate, this work being done with a small car- 

 borundum grinder. After a host larva and a parasite &g<y had been 

 placed in a hollow, the cell was closed by covering it with an ordinary 

 glass cover slip. The cover glass was held in place by two little dabs of 

 honey on its underside. The cell was not sealed by a complete ring of 

 the adhesive because of the desirability of diffusion of atmospheric 

 moisture under the cover slip. Honey seemed to be the ideal adhesive 

 for this purpose, since it had no odor harmful to the inmates of the cell; 

 it held the cover-glass tight against the slide; it did not dry so hard as to 

 prevent the cover-glass from being easily removed; and a supply of it 

 was always convenient. A label was pasted on the glass plate near one 

 end for identification. The complete development of the parasite from 

 egg to adult on its host could then be observed under the binocular in 

 this little cell without disturbing the parasite or the host in the least. 



With each of the three species the period from oviposition to emergence 

 of adult, when individuals were reared in glass cells, approximated very 

 closely the period from egg to adult when individuals were reared under 

 the same meteorological conditions in Hessian-fly flaxseeds. Hence, the 

 length of each stage of development as determined from individuals 

 reared in glass cells may be considered normal. 



It was discovered that the lar\^ge of all three species molted while making 

 their growth within the little cells. The length of the instars was not ob- 

 serv^ed, but the number of molts was determined by transferring to a balsam 

 mount on a microscope slide all the material left behind in the little glass 

 cell where a single individual had made its growth. In cases where the 

 larva had pupated, the last molted skin was added to the mount. In 

 cases where the full-grown larva had not pupated, the mandibles borne 

 by the larva were dissected from it and added to the mount. To deter- 

 mine the number of molts of a single individual, the mount of the material 

 it left behind was examined under the microscope and the number of 

 pairs of mandibles in the material ascertained. In all cases the cell in 

 which the larva made its growth was known to be absolutely clean when 

 the host and the e:gg from which the parasite larva hatched were placed 

 in it ; hence, it was known that all pairs of mandibles found in a mount 

 belonged to the same larva. Cells which contained simultaneously the 

 remains of more than one parasite larva were not used in determining the 

 number of molts. No attempt was made to determine the number of 

 molts of individuals which had made their growth inside flaxseeds. 



