53O HYMENOPTERA CHAP. 



About fifty years ago Hartig reared large numbers of certain 

 species of gall-flies from their galls, obtaining from 28,000 galls 

 of Cynips disticha about 10,000 flies, and from galls of C.folii 

 3000 or 40 examples of this species ; he found that all the 

 individuals were females. His observations were subsequently 

 abundantly confirmed by other naturalists, among whom we 

 may mention Frederick Smith in our own country, who made 

 in vain repeated attempts to obtain males of the species of the 

 genus Cynips. On one occasion he collected in the South of 

 England 4410 galls of C. kollari (at that time called C. ligni- 

 cola), and from these he obtained 1562 flies, all of which were 

 females. A second effort was attended with similar results. Hartig, 

 writing in 1843, after many years' experience, stated that though 

 he was acquainted with twenty-eight species of the genus Cynips, 

 he had not seen a male of any one of them. During the course 

 of these futile attempts it was, however, seen that a possible 

 source of fallacy existed in the fact that the Insects were reared 

 from collected galls ; and these being similar to one another, 

 it was possible that the males might inhabit some different gall. 

 Adler endeavoured to put the questions thus raised to the test 

 by means of rearing females from galls, and then getting these 

 females to produce, parthenogenetically, galls on small oaks planted 

 in pots, and thus completely under control. He was quite 

 successful in carrying out his project, and in doing so he made a 

 most extraordinary discovery, viz. that the galls produced by these 

 parthenogenetic females on his potted oaks, were quite different 

 from the galls from which the flies themselves were reared, and 

 were, in fact, galls that gave rise to a fly that had been previously 

 considered a distinct species ; and of this form both sexes were 

 produced. Adler's observations have been confirmed by other natu- 

 ralists, and thus the occurrence of alternation of generations, one 

 of the two generations being parthenogenetic, has been thoroughly 

 established in Cynipidae. We may mention one case as illustrat- 

 ive. A gall-fly called Cliilaspis lowii is produced from galls on 

 oak-leaves at Vienna at the end of April, both sexes occurring. 

 The female thereafter lays eggs on the ribs of the leaves of the 

 same kind of oak, and thus produces a different gall from that 

 which nourished herself. These galls fall off with the leaves in 

 the autumn, and in July or August of the following year a gall- 

 fly is produced from them. It is a different creature from the 



