140 AMERICAN HYMENOPTERA. 



liquid mass. This indicates that this parasite is kept in check 

 by some disease that reaches it within the body of the host." 

 Investigations at the Gypsy Moth Laboratory show that 

 macrurus is often the victim of other parasites of the same 

 host, or of secondary parasites. 



Variation. — The members of this genus seem to be among 

 the most variable of the American representatives of the 

 tribe. Variation in size and venation is quite marked, espe- 

 cially in E. niacrurtis L. Here the size runs from 22-36 

 mm. ; the color varies from ferruginous to flavous with all 

 intermediate gradations ; the wings vary from a complete 

 fulvous to hyaline — the color seems to be most permanent 

 at the base, disappearing first at the apex and working to- 

 wards the body. Variation in color works, as always, in two 

 directions, (1) towards the light or albinic and (2) towards 

 the dark or melanic. Most specimens are fulvo-ferruginous, 

 with a distinct fulvous tinge in the wings, but throughout 

 the entire range there are always a few of the light forms. 

 These seem to be more numerous, however, in southern 

 United States and Mexico. The melanic forms do not seem 

 to show as great variation, but E. texanus greatly resembles 

 macruriis, and may prove to be a melanic form. Its fuscous 

 wings and dark ferruginous body, more or less marked with 

 black, seem, however, to be sufficiently fixed to be con- 

 sidered specific, yet this can not be finally settled until breed- 

 ing experiments have been carried on. In venation the 

 radius may be as in macrurus, enlarged at the base and in 

 some specimens doubly bent, but a good series generally 

 shows a gradation to the once-bent condition seen in E. 

 arcticB. In macrurus, angulatus, and flavofuscus the radial 

 vein is angularly broken about 1 mm. from the stigma. The 

 angularly broken radial vein is, I believe, the older condi- 

 tion, showing where the first transverse cubital nervure 

 branched off. Breeding experiments may show that arctice is 

 only a subspecies of inacrurus, but the species as I have re- 

 stricted it seems to have well fixed characters. The varia- 

 tion in size may be easily explained by a difference in the 

 amount of food supply of the larva. Similar variation in 



