184 



Dr. L. Doncaster. Gametogenesis and 



some support from the fact that in the spermatogenesis an extra-nuclear 

 body was observed not to divide at the single spermatocyte division, but to 

 pass over into one of the two spermatids. 



Further investigation of the matter was interrupted by other work until 

 1913, but in that year I determined to test the hypothesis mentioned by 

 rearing the offspring of individual sexual females separately, and then 

 finding whether each family contained both male-producing and female- 

 producing individuals. If they did not, that is to say, if the offspring of 

 any one sexual female were all male-producing or all female-producing, the 

 hypothesis that the difference depended on two kinds of spermatozoa would 

 be disproved, for the receptaculum seminis of the fertilised female should 

 contain both sorts of spermatozoa, and therefore both kinds of fertilised 

 eggs should be laid by the one female.* At the same time I determined to 

 test afresh the possibility that the two kinds of agamic females were derived 

 respectively from fertilised and parthenogenetic eggs laid by the sexual 

 females. This seemed very improbable, for in almost every egg of the 

 sexual generation examined for the maturation divisions, a spermatozoon 

 was found, and it was therefore almost certain that all the eggs of the sexual 

 generation are normally fertilised. 



For the purpose of these experiments a number of females of the sexual 

 generation were sleeved on oak twigs in May, 1913, one female in each 

 sleeve. Some of the females used had been seen to copulate with males ; in 

 other cases two or three males were enclosed in the sleeve with the female 

 so that fertilisation would almost certainly take place, and finally a number 

 of virgin females, from galls kept separately so as to make the access of 

 a male impossible, were also sleeved on other twigs of the same oaks. In 

 several instances virgin females laid eggs in the leaves, but in no case was 

 a gall produced, and the eggs appear either not to have developed at all or 

 to have died at a very early age. It may, therefore, be taken as certain that 

 females of the sexual generation do not reproduce parthenogenetically. 

 Of the fertilised females, about a dozen produced galls on the leaves, some 

 of them in considerable numbers. These galls were allowed to grow until 

 ripe in October, then collected and kept separately through the winter. In 

 February and early March a number of branches of an oak tree were covered 

 with large muslin sleeves to prevent the access of wild flies, and when the 

 galls were about to hatch they were placed in sleeves on the branches which 

 had been covered, and also in some cases on uncovered branches, since the 



* If there were two kinds of males, producing different spermatozoa, the result under 

 consideration would still be obtained if each sexual female paired with only one male. 

 This hypothesis is further considered later. 



