XXIII.—The Cytology of the Thelytokously Parthenogenetic Saw-Fly Thrinax macula Kl

Abstract

Since the preliminary cytological work of Doncaster (1906) nothing has been recorded on the maturation of the thelytokously (female-producing) parthenogenetic saw-flies (Ten-thredinidæ). Doncaster worked with the four species now known, according to Enslin (1918), as Empria abdominalis F., E. pulverata Ritz., crœsus varus Vill., and Hemichroa crocea Geoffr., and he concluded (1907) that the chromosome number in the oocyte, polar nuclei and egg pronucleus was 8, there being two maturation divisions giving rise to an egg pronucleus and three polar nuclei. As stated in our note to Nature (1937) recent work on the thelytokously parthenogenetic species, Pristiphora pallipes Lep., by our colleague, Mr L. C. Comrie, confirms Doncaster regarding the number of maturation divisions and polar nuclei, but raises strong doubts on Doncaster's interpretations of chromosome number and behaviour. Doncaster did not make it clear whether the diploid number was 8 or 16, or whether auto regulation occurred during or after maturation. It appears probable that the real diploid number is 16, for intensive study of over twenty species of saw-flies, carried on mainly by Dr F. Greenshields in this department (unpublished work), shows that the characteristic diploid number for Tenthredinidæ is 16. Further, judging by Mr Comrie's research on Pristiphora pallipes, in which the diploid number is also found to be 16, it would appear probable that autoregulation in Doncaster's types is brought about by fusion of egg pronucleus and second polar nucleus.