THE IMAGO. d 



extra length of time being taken up with the agamic 

 winter form. The development of this gall is not con- 

 tinuous ; for in October, or month following the laying 

 of the eggs, a slight growth takes place, followed by 

 a cessation of development during the winter, owing 

 to the inactive growth of the plant, to be resumed in 

 the spring. A curious point is that in many winter 

 forms cases are met with wherein the larvae remain 

 unchanged for several years. I believe this is fre- 

 quently the case with Andricus gemmae and A. glandium. 

 How far this is owing to atmospheric influences or to 

 more subtle causes it is difficult to say. 



The Pupa 



is, like the larva, white and fleshy. It has the an- 

 tennas placed along the breast, the legs alongside of 

 them enveloped in pellicles, and the wings appear as 

 bag-like protuberances on the sides of the thorax. 



The Imago. 



Apart from their peculiarities of oviposition, which 

 offer interesting features, the flies do not show many 

 points of interest. They are exceedingly sluggish, 

 seldom flying any distance. So far as we know they 

 take no food, and do not frequent flowers like so many 

 of the parasitic Cynipidae. They do, however, imbibe 

 water, as may be often witnessed. Many of them 

 have a habit, when alarmed, of tucking the appendages 

 close to the body and dropping motionless to the 

 ground. 



A noteworthy point is that some of the species, e. g. 

 Biorhiza aptera, appear in the dead of winter during 

 snow and frost, and even with the atmosphere at 

 freezing point proceed to lay their eggs. 



The males differ from the females in having the 

 antennae longer and thinner, and in having one or 

 two joints more ; there is no difference in coloration, 



