92 THE GENETIC AND THE OPERATIVE EVIDENCE 



that produces it under the influence of the parasite. Incidentally, as 

 it were, this is said to be the same yolk-substance (but no sufficient 

 evidence that it is the same is given) that the egg stores up inside itself, 

 and it is assumed that it is a formative substance that causes the cell 

 that gets it (or contains it or secretes it — details are wanting) to 

 become an egg-cell. It is the excess of this substance produced by the 

 male crab, while still a male, under the influence of the parasite, that 

 affects the abdomen and its appendages in such a way that they assume 

 the female condition. There are too many assumptions in the argu- 

 ment, some of which are scarcely of a kind that our knowledge of 

 development, incomplete as it is, can allow us to accept without more 

 direct evidence in their support, to make this view very plausible. 

 Until better evidence is forthcoming, I fail to be convinced by Smith's 

 interpretation of his facts. 



Into Smith's and Robson's interesting observations on the blood of 

 crabs, described in Smith's later paper (part 7, 1911), it is not necessary 

 to enter here, since the evidence taken as a whole offers little further in 

 support of his view than had been already assumed. The argument on 

 page 263 should not, however, pass unchallenged. Smith says: 



"It is clear that the old and familiar idea of an internal secretion produced 

 by the gonad being the stimulus for the development of the secondary sexual 

 character could not be applied here, since at the time that the alterations in 

 the secondary sexual characters take place no ovary is present to give rise 

 to the required stimulus. It is suggested, therefore, that in some way the 

 stimulus must reside in the roots of the Sacculina," etc. 



The argument seems to imply that, since the secondary sexual 

 characters of the female can not be produced by an ovary in the infected 

 male, therefore the Sacculina must take the place of the ovary. But 

 why make such a supposition, for if the testes simply keep down the 

 development of the female characters, as Giard supposes, there is no 

 need either for an ovary or for a Sacculina to develop them. One might 

 as well argue that since the cock does not develop the secondary sexual 

 characters of the hen that an ovary is essential for their development — 

 which is true, but not in the sense implied. 



Stamati (1888) states that he attempted to remove the testes of 

 adult crayfish and apparently succeeded, but since no effects are 

 expected until after a molt occurs (that may not take place for two 

 years or more), no results were obtained. Injections of the gonads 

 with an acid failed, since the animals died. 



E. Evidence from Insects. 



In 1899 Oudemans succeeded in finding a method of removing the 

 testes and ovaries from caterpillars, using a dimorphic species, Ocneria 

 dispar, the gipsy moth. The results were negative; none of the secon- 

 dary sexual characters of the male or female moths or the accessory 

 organs of copulation were in the least affected by the operation. The 

 castrated male copulated as readily with the female as did the normal 



