Biorhiza Group. 141 



living from two to four weeks. Several of the summer 

 flies are very fragile and do not live many days. 



The whole energies of the Cynipidae are devoted to 

 the proper deposition of their eggs. The more easily 

 and quickly the eggs can be laid, the shorter is the life of 

 the individual ; this we see exemplified in Spathegaster. 

 If on the contrar}' the act of egg-laying is difficult, and 

 demands much physical exertion, the gall-flies are 

 stronger and live longer ; the winter generations, which 

 always have the troublesome task of la^'ing their eggs 

 in buds, have consequently a much more vigorous 

 organization than the correspondingsummer generations, 

 and this also enables them to resist the inclemency of 

 a ruder season. A Biorhiza aptera fly can prick a bud 

 with the thermometer at freezing point ; its summer 

 generation, Teras terminalis, would undoubtedly be 

 frozen by the same degree of cold. 



Lastly it is important to compare the reproductive 

 organs in the two generations. Here a perfect analogy 

 will be found to exist ; the ovaries have the same 

 structure, each contains a corresponding series of 

 ovarian follicles, in which there lie from six to twelve 

 eggs. In a general way the agamous generations have 

 a larger number of eggs than the sexual, and as a rule 

 the number of follicles, as well as the number of the 

 enclosed eggs, is greater. 



The muscular vagina, with its glandular appendages, 

 is the same in the two generations. On each side, near 

 the oviduct, a simple glandular tube opens into the vagina. 

 Its secretion probably only serves to furnish a liquid 

 suited to receive the spermatozoa as they escape from 



