192 Summary of Evidence as to Sex [CH. 



differences even in nearly allied forms, some having a 

 distinct unpaired chromosome, while in others this body is 

 either fully or imperfectly paired. In Lepidoptera, as it 

 happens, the accessory chromosome has not been found. 

 Improbable as at first sight it may appear, the view that 

 most commends itself to me is that in different types Sex 

 may be differently constituted. From the results of castra- 

 tion-experiments we are led to a similar view ; for castration 

 of the male Vertebrate on the whole leads merely to the 

 non-appearance of male features, while injury or disease of 

 the ovaries may lead to the assumption of male characters 

 by the female. In Crustacea the evidence of Geoffrey Smith 

 and Potts shows that these consequences are there reversed. 

 The great diversity of cytological features in allied Insects 

 is also consistent with the expectation that the phenomena 

 are specific rather than universal 



Then again we may feel fairly sure that the allelo- 

 morphism between the sex-characters must be a relation of 

 no common order. The curious numbers that so often 

 occur in collections of sex-ratios are evidence of this. The 

 records given in the case Aglia tau and lugens bring us at 

 once to difficulties with which as yet we cannot deal. 



From time to time evidence has been advanced to show 

 that the production of the sexes can be influenced by special 

 modes of nutrition or other environmental influences. An 

 adequate discussion of this evidence would run to great 

 length. Some of the evidence has been found faulty in 

 various respects*, and I am not aware that any example has 

 been confirmed by successive observers in such a way as to 

 warrant definite belief in its validity!. It is not impossible, 



* See for instance Punnett (227) on sex-determination in Hydatina 

 with a criticism of the evidence of Nussbaum on the positive effects of 

 nutrition. 



t The most striking case in which positive results are said to have 

 been attained is that lately published by Russo (236). This observer 

 claims to have demonstrated in the rabbit the difference between the ova 

 destined to become females and those destined to become males. His 

 conclusion is so far in harmony with that to which genetic experiments 

 have led us, that the female is heterozygous in sex. Heape, however, has 

 described (Proc. Roy. Soc. vol. 76, B, 1905) in the rabbit processes by 

 which ovarian ova frequently degenerate, apparently as a normal occurrence. 

 Mr Heape very kindly gave me an opportunity of examining his prepara- 

 tions, and it was impossible to avoid being impressed with the general 



