88 



Gametogenesis of the Gall-Fly, Neuroterus lenticularis (Spathe- 



gaster baccarum). — Part 1, 

 By Leonard Uoncaster, M.A., Lecturer on Zoology, Birmingham University. 



(Communicated by Prof. W. Bateson, r.R.S. Received September 21, — 

 Read December 9, 1909.) 



[Plates 1—3.] 



In previous papers* I have described the maturation of the egg, with some 

 observations on the spermatogenesis, of the Saw-fly, Nematus ribesii, in which 

 the eggs may develop either parthenogenetically or after fertilisation. Some 

 questions remained obscure or doubtful, and it seemed probable that an 

 answer to them might be found in a study of one of the gall-flies (Cynipidte). 

 The gall-flies are remarkable in having in most species two generations 

 in the year, of which one is bisexual, and the other consists wholly of 

 females. The flies of the two generations are, further, so difl'erent from one 

 another in structure that in most species they were originally described as 

 belonging to different genera. The galls produced by the two generations 

 are also very distinct. 



The species chosen for this work was the very common Neuroterus 

 lenticularis, of which the sunmier (bisexual) generation was originally 

 described as Spatlmjdster baccarum. The galls from which the spring 

 (agamic) generation emerge are lenticular growths found on the underside 

 of oak leaves in October. From these galls the flies hatch early in April ; 

 they are exclusively females, and, if provided with buds of oak, readily lay 

 their eggs deep down among the developing leaves and catkins. The eggs 

 were dissected out, fixed in Petrunkewitscli's mixture (alcohol-acetic- 

 .snblimate) at various times after being laid, and cut into sections. 



The galls of the summer form are spherical, sappy galls, found on the 

 leaves and catkins in May and June. From them hatch males and females 

 <thc latter in nature largely pieponderating in number), and after copulation 

 the females deposit their eggs in the tissue of young leaves, always at the 

 .side of a small vein. The f(!niales of tliis gentiration differ considerably from 

 the agamic fcrnaloH of the H])ring brood. Tlie most 0()nK])icuous diffcu'encc is 

 in the ovipositor, whicli in the summer females is (juito short, l)ut in the 

 againic females is fully five times as long, and coiled uj) in the abdomen. 

 The flies lay readily, and the eggs may be seen with a lens, so that small 



* 'Q.J.M.S.,' vol. 4!), IDOfJ, p. r)(;i, ;in(l vol. 51, 1907, p. 101. 



