Manchester Memoirs, Vol. Ixii. (191 7), No. 2 23 



accordance with the theory. The rare occurrence of males is of 

 interest, but at present we are entirely ignorant as to whether there is 

 any difference in the maturation of those eggs from which males 

 are produced. It may be that the males develop as in the bee, 

 or there may be non-disjunction where the sex chromosomes 

 are extruded with the polar nucleus. 



Lastly, the case of the Aphids must be considered. No re- 

 ductive division occurs in the parthenogenetic eggs, but the 

 males and females are hatched from them. In all cases investi- 

 gated, however, the eggs from which males develop eliminate one 

 or more chromosomes, which are retained in female-producing 

 eggs. 



Wilson has himself pointed out that in plants both males jand 

 females are formed from asexual spores, and that these spores 

 usually contain the haploid chromosome number. This of course 

 seems to be contrary to the theory, but it is possible that the 

 male-producing ones may be characterised by the absence of one 

 or more elements found in the female 'spores. 



Goldschmidt (1917) put forward a view almost identical with 

 the theory given above. He believes that the production of sex 

 is a quantitative phenomenon due to two factors, one of which 

 is carried in the sex chromosome!, the other by the cytoplasm 

 of the egg. His reasoning is practically the same as that of 

 Wilson. The chief importance of the suggestion is the possi- 

 bility that the cytoplasm may be a carrier of inherited qualities. 

 There is much evidence for this belief, 'but there is also a ten- 

 dency to regard the nucleus as the only factor of importance in 

 the study of problems of heredity. Thfs lis a mistaken idea, and 

 if the cytoplasm be excluded from all study, advance in our know- 

 ledge of the laws of heredity will be diminished. 



The evidence given in a previous part of the paper is suffi- 

 cient to show that the sex of an individual is affected by external 

 conditions, but there is also reason to believe that internal factors 

 exert a very definite influence on sex production. The proba- 

 bility is that these ftwo sets of factors act together. The experi- 

 ments of Geoffrey Smith are of importance in this connection. 

 He found that as a result of parasitism by Sacculina male crabs 

 assume the female characters and may even produce ova in the 

 testes. Further, he demonstrated that metabolic changes 

 occurred during the parasitism with the result that the meta- 

 bolism of the affected male became almost identical with that (of 

 the normal female. Great differences are also> known to exist 

 between the blood of male and female of the same species of 

 many Lepidoptera. Observations such as these give rise to the 

 suggestion that the differences between the two sexes are those pf 

 metabolism. As Doncaster says in his paper, " Chromosomes, 

 Heredity and Sex," the general conclusion must be that although 



