496 Journal of Agricultural Research voi. v, no. 12 



the point of the smaller end to assume the appearance of a nipple-like 

 prominence. 



The number of eggs laid by a single individual was not obtained, 

 nor were the eggs in the abdomen counted, hundreds having been present. 



EMBRYONIC DEVELOPMENT 



The average length of the &gg stage is $^2 days. Individual records 

 show that in some cases this may be shortened to 4^ days or prolonged 

 to more than 6% days. From the hundreds of developing eggs exam- 

 ined it was determined that only one larva hatches from each egg. 



Development progresses rapidly within the egg. At first little can 

 be distinguished, except that the &gg becomes strongly curved, increases 

 in size, and becomes more opaque, owing to the formation of the germ 

 band. When the e^gg is ready to hatch it has increased in size from 

 0.09 or o.io mm. in length to 0.66 or 0.70 mm., and proportionally in 

 width. This great increase in size can possibly be explained by the 

 fact that the egg is probably deficient in nutritive matter when laid 

 and that this is absorbed from the blood of its host by the developing 

 embryo. 



When embryonic development has progressed sufficiently to show the 

 form of the embryo, this is seen to be surrounded by a single embryonic 

 envelope one cell layer deep which, according to Korschelt and Heider 

 (3, p. 287),^ is the serosa (PI. L, fig. i). Whether the amniotic and 

 serosal envelopes are at first separate has not been determined. Accord- 

 ing to Graber's observations on Hymenoptera, as reviewed by Korschelt 

 and Heider, it would seem that the two envelopes are separate at first 

 but later become indistinguishably united. At the time of hatching, 

 a portion of the cells of this so-called serosal envelope are cast out at the 

 poles of the ^gg (PI. L, fig. 2) and become a body of loose cells lying 

 between the chorion and the embryo (PI. L, fig. 3), which is now tightly 

 inclosed by a layer of broad, flattened cells made up of the remaining cells 

 of the envelope (PI. L, fig. 3). This rapid division apparently indicates 

 that this envelope was the product of the fused amnion and serosa, which 

 now separate at hatching time, the loose mass of cells being of serosal 

 origin and the remaining thin envelope the amnion surrounding the 

 embryo. Henneguy (2, p. 336-337), however, discusses insects that have 

 only one embryonic envelope and lists among these parasitic forms, vege- 

 table or animal, of the Cynipidae, Pteromalidae, and probably Ichneu- 

 monidae. It will be interesting to note whether other investigators 

 observe this splitting of the single embryonic envelope at hatching time. 



The mandibles can be seen forming at an early stage, and their chitini- 

 zation can be seen to progress until maturity is reached at hatching time. 



' Reference is made by number to "Literature cited," p. 506-507. 



