466 SCIENCE PROGRESS 



while the same influence on the female produces only a reduction 

 of the female characters. The facts do not seem to me to justify 

 this conclusion, or to indicate that the relations of the sex- 

 characters in Brachyura are in any way different from those 

 which obtain in Vertebrates. It is true that the crab infected 

 with Sacculina has the appearance of a female, and at one time 

 it was supposed that only females were attacked by the parasite ; 

 but it is now known that the Sacculina sterilises the testes, and 

 that as a consequence the male characters are not developed. 

 The chief result is the reduction of the size of the chelae, which 

 are normally much larger in the male than in the female. This 

 is no more the assumption of a female character than the 

 suppression of the antlers in castrated stags. The breadth of 

 the tail, however, is increased ; and this is the point which Smith 

 regards as showing the development of the female character, 

 because the tail is normally broader in the female in adaptation 

 to its function of bearing the eggs. But the narrowness of the 

 tail in the male is a secondary character, and therefore suppres- 

 sion of this character means the broadening of the tail ; while in 

 the female the special egg-bearing character of the tail is reduced, 

 so that the structure is brought to a similar condition in both 

 sexes. When the male recovers from the attack of the parasite, 

 eggs are found in the gonad ; so that there is no doubt that the 

 female sex is latent in the male. I do not dispute this conclusion, 

 but merely maintain that it is equally true of Vertebrates. I 

 consider, however, that the evidence for the absence of the male 

 sex from the female crab is insufficient. 



Mr. Doncaster claims that the Mendelian hypothesis which 

 he describes " not only explains the cases which led up to it, 

 and such facts as the effects of castration, but also accounts for 

 the phenomena of sexual dimorphism and the inheritance of 

 some structures by one sex only." It is sometimes maintained 

 that Mendelism deals only with the facts of heredity. It is 

 perfectly true that it deals with some facts of heredity; and the 

 present writer has no desire to deny the facts proved by 

 Mendelian experiment, or to depreciate their importance. But 

 Mendelism does not confine itself to facts — it consists very 

 largely of theory. Setting out from the simple inference that 

 the separation of the members of a pair of characters in the off- 

 spring of hybrid parents is due to segregation of those characters 

 in the gametes, it proceeds to invent a new formula for the 



