PARTHENOGENESIS. 317 



Parthenogenesis. — Report of Committee (Professor A. Meek, 

 Chairman; Mr. A. D. Peacock, Secretary; Mr. R. S. Bagnall, 

 Dr. J. W. Heslop Harrison). 



The objects of this reseaixh were investigations into the biological and 

 cytological plienomena of parthenogenesis in sawflies of the family of 

 Tenthredinidcr. 



Some forty species have been collected wild or obtained through, the kindness 

 of Miss E. F. Chawner, Lyndhurst, Hiiints, and reared in the laboratory 

 in order (1) to develop a technique, (2) to acquire diverse material for 

 ascertaining how far parthenogenesis is a feature of sawfly biology, and (3) to 

 make a selection of species particularly amenable to experiment. 



Attention is being particularly focused on the following species : Allantus 

 (Eiiifhyfvi^) jiallipcs Spin.; Pristiphora pallipcs Lep., which produce only 

 females by parthenogenesis, and Croesus septentrionnlis L. ; Pieronidea ribesii 

 Scob., which produce only males parthenogenetically, but the species Nematinus 

 luteus Panz., Holocneme lucida. Amctastegia (Taxonus) glahrata Fall., 

 Phrpnatocern aterrima Kl., Pteronidea pavida Lep., P. melanaspis Htg., 

 Thrinax mixta Kl. and T. macula Kl. are also under close observation. 



The result.s to date may be summarised as follows, the observations on 

 parthenogenesis being noted first as they form the object of the inquiry : — 



Parthenogenesis. 



[a] New Parlhenogeni'lic Species. — The following seven species as additions to 

 the lists of Cameron and Enslin are brought forward as facultatively partheno- 

 genetic : (1) Nematinus lutctis Panz., (2) N ematinus ahdominalis Panz. nee F., 

 Platycampus luridiventri.t Fall., (4) Thrinax mixta, (6) Pteronidea poecilonota 

 Zadd. , (7) Dolerus aeneus. Htg. 



As experimentation proceeds others will undoubtedly be added. 



(h) Number of Consecutive Parthenogenetic Generations. — Allantus 

 [Emphytus) paUipes has been reared for four generations and Pristiphora 

 pallipes for four generations. In both cases no male was reared. The strains 

 are being maintained. 



(c) Pairing and Egg-laying flahits. — The most important breeding results 

 to date concern observations on Phymatocera aterrima and Nematinus luteus. 

 The females of l>otli species, after laying eggs parthenogenetically, were found 

 to pair with the male. After such laying and pairing more eggs were obtained 

 from A^. luteus, but, owing to the enforced use of alder twigs instead of young 

 trees (the supply having been exhausted), this second batch of eggs, presumably 

 fertilised, was not hatched because the twigs wilted. The females of P. aterrima 

 were observed to be almost spent before pairing, and their failure to lay a 

 second, and possibly fertilised, batch of eggs did not occasion surprise. 



These experiments suggest that the sam3 female sawfly may reproduce both 

 parthenogenetically and sexually, dependent upon its rejection or acceptance of 

 the male. Further work is proposed this summer and autumn, utilising suitable 

 snecies, with a view to ascertainino; (1) how far this practice obtains among 

 sawflies ; (2) how it affects the production of the se.xes and ipso facto the sex 

 ratio; (3) the chromosome complement of offspring resulting from the two 

 different batches. Should the practice be widely spread in this family, much 

 light will be shed upon other curious phenomena among sawflies, viz. the 

 ignoring of the males by the females (or vice versa) in certain species : the 

 parthenogenetic production of males only in certain species ; the rarity of males 

 in certain species. 



Gametogenesis. 



A large amount of material — about eighty tubes — has been preserved for 

 cytological work on the species under particular observation. (Sec above.) 



The labour of carrying on breeding experiments dnriiic the season, May- 

 September, forbids much else than the collection of material, but a certain 

 number of slides illustrating oogenesis in Allantes pallipes and Pristiphora 

 paUives and spermatogenesis in Thrinax mixta have been made and preliminary 

 readings noted. Certain of the gross features of oogenesis and the behaviour 

 of the nucleolus in regard to budding have been observed, but the finer work 

 on chromosomes has barely been touched. 



