xlii Obituary Notices of Felloivs deceased. 



hybridization of Echiuids — a problem which had naturally acquired fresh 

 interest from the recent discovery of the Mendelian system of analysis. 

 Up till that time the observation that a cross between two species did not 

 give a uniform result was accepted without demur, but now such an occur- 

 rence was anomalous, and called for special consideration. A great deal 

 still remains to be done in this vexed field. Doncaster, however, was 

 successful in contributing one new fact, namely, that the seasonal changes 

 observed by H. M. Vernon were in the main directly dependent on tem- 

 perature. His experiments, which were very laborious, also demonstrated 

 a curious series of individual differences in the degree of dominance — a 

 phenomenon which should be examined further. 



On his return to England he attached himself definitely to the group 

 of studies now called genetics, and began a number of investigations, most 

 of which involved experimental breeding. At various times he bred rats, 

 cats, pigeons, besides gall-flies, moths, and other invertebrates. The early 

 struggles of Mendelism to obtain a hearing were then in an acute stage, 

 and though strongly inclined to caution, he knew enough of the general 

 course of variation and heredity to be in no doubt as to the essential truth 

 of the new doctrines. His adhesion certainly helped greatly in spreading 

 confidence among his contemporaries. His first paper on a definitely 

 Mendelian problem was a note on the Tortoise-shell Cat, in which he 

 showed that the well-known rarity of tortoise-shell tom-cats is an expression 

 of the fact that whereas the cross between orange and black produces female 

 tortoise-shell, the corresponding male form is orange. About this time he 

 began an investigation into the life-history of the saw-fly, Nematus ribesii, 

 and of the gall-fly, Neurotems lenticidaris. The latter subject he pursued 

 with intervals for more than ten years. The purpose was to discover the 

 mechanism by which sex was determined in these species. The fertilized 

 eggs of Neuroterus give rise to females only, as do those of Phylloxera and 

 some other Hemiptera. These females, imfertilised, produce other females 

 of which (again without fertilisation) some produce males, and others females, 

 not a mixture — a condition now known to be parallelled by various insects. 

 The cytological distinction, if there is one, between these two types of 

 females, is still xindiscovered. Doncaster 's work on these and similar types, 

 and especially the clear exposition which he gave of their intricate poly- 

 morphism, contributed much towards the comprehensive codification by 

 which a mass of apparently contradictory records as to the partheno- 

 genetic or agamic and sexual forms of Hymenoptera and Hemiptera has been 

 reduced to order. 



He will be, however, best remembered for his experiments on the 

 inheritance of sex in Abraxas grossulariata, the Currant Moth. From the 

 Eev. G. H. Eaynor, who had long been a fancier of this species, Doncaster 

 learnt that the variety lacticolor, distinguished from the common form by 

 a great reduction in the amount of black, was known only in the female. 

 At that time no example of what is now called " sex-linked " inheritance 



