NOTES ON PHYTOPHAGOUS HY3IEN0PTERA ISOO -1900. 19 



by a ? in whose ovary no trace of spermatozoa is discernible, will 

 produce imagines at the rate of, in some cases, 172 J s to a single 

 $ , and often a whole brood will produce no ? at all. Occasionally, 

 however, parthenogenetically deposited ova prove infertile, and at 

 other times, after the first generation, there is usually increased 

 mortality, and in those kinds having the sexes fairly equally divided 

 in the first, ^ s Avill be greatly in preponderance in the second 

 generation. Kirby and Spence first discovered this phenomenon, and 

 interesting papers have subsequently been published upon the subject 

 by Professor Owen {ParthoKKjcucsis, 1H1<J), Huxley [ReprodHction of 

 Aphis, TrauH. Linn. Soc, vol. xxii.), Von Siebold (Kssai/ on Partheno- 

 (/encsis, Leipzig, 1871, &c.), Geddes and Thompson {Kcolittion o/iSV,v), 

 Cameron (I.e.), &c. 



Although the TentJircdinidae seem to have been so greatly neglected 

 before the present century, this was not the case with the gall insects, 

 or rather with the galls caused by them. Our own countryman, Sir 

 Thomas Browne, about the middle of the seventeenth century, seems 

 to have paid much attention to the galls, more especially those of the 

 oak, as appears from his letters to Dr. Merritt, the author of Finax 

 rcruin XaturaliiDn Britannicaruin (London, 1G66). A good propor- 

 tion of the galls mentioned by him are easily recognisable. But 

 the first person who gave an accurate description of galls appears to 

 have been Malpighi, who published his book {Dc (rallis) in 1G86, 

 while Dr. Derham, Canon of Windsor, soon after compared 

 Malpighi's account with the galls found by him in England. Until 

 long after this, however, little seems to have been done in the classifi- 

 cation of the makers of the galls, till in the middle of the present 

 century great improvements were made in this respect by Hartig, of 

 Brunswick, 1840-43. He not only revised the classification, but care- 

 fully distinguished, first the real gall makers, secondly the inquilines, 

 or guest-fi.ies, which live on the substance of the gall, though not 

 upon the Cynipid larvae, and thirdly the parasites which feed on the latter. 



Since that time the interesting discovery has been made of an 

 alternation of generations in many species of gall-flies. It was always 

 a puzzle what, in many cases, became of the flies when disclosed from 

 the galls. Thus, for example, the imago leaves the currant gall early 

 in the summer, yet no more currant galls are seen until late in the 

 following spring, and not only is this the case, but in many supposed 

 species none but females were known. In 1877 Hermann Adler began 

 his investigations, and proved that there were alternate generations, 

 the insect from the currant gall causnig the common spangle gall, 

 while the insect from this gall, being disclosed in the spring, was the 

 maker of the currant gall. Again, one of these generations con- 

 sisted of both males and females, the other of females only, while the 

 insect of one generation differed so materially from that of the other 

 that they had been considered to belong to ditt'erent genera. Adler 

 continued his investigations, and proved that this was true of many 

 other species. Thus Avas it shown that there were alternations of 

 generations and dimorphous females {<;/'., Adler, La ijcnc ration 

 alternantc clic:: Zc.s Ci/nipidcs, 1881). It is not so, however, with all 

 the Cynips gall-makers. In some cases there appears to be one 

 generation, and that of females only, hence we have here complete 

 parthenogenesis and an apparently endless succession of females. 



