in the Decapod Cruslacea. 339 



the opposite sex, ready to he evolved under peculiar circum- 

 stances^ 



Examples of a similar abnormal development of the charac- 

 ters of one sex in the op)josite sex are not unknown among 

 the Crustacea. Grobben * has several times met with females 

 of Astacus Jluviatilis in which the first pair of abdominal feet 

 were constructed as in the male. The ovaries were well 

 developed, and these females bore ova upon the other feet. 

 Grobben interprets the fact as a simple transfer of the charac- 

 ters of one sex to the other, which, he adds, is not uncommon 

 in the animal kingdom. 



E. von Martens has noted the presence of female genital 

 apertures in the male of Astacus pleheius f. Hilgendorf has 

 likewise ascertained the presence of rudimentary female 

 genital orifices upon the third pairs of feet of the males of 

 certain Crustacea |. 



We may remark that in the case of the crabs infested by 

 Sacculinoi there is not in reality, as we have already pointed 

 out, any manifestation of female characters in the male sex, 

 but rather an absence of the development of the male charac- 

 ters ; the animal remains in a young stage, not sexually 

 differentiated, but acquiring a somewhat larger size. Tiiis is 

 also, in our opinion, what occurs in castrated mammals and 

 birds. While the females whose ovaries have been destroyed 

 or no longer function acquire the positive characters of the 

 male sex (horns, spurs, hackles, &c.), the castrated males are 

 modified especially in this direction, that they do not acquire 

 the attributes of their sex. It is true that it may be remarked 

 that m the cases cited by Darwin, as in that of the Sacculi- 

 niferous Crustacea, it is the female that most closely approaches 

 the stock-form and presents the fewest secondary sexual cha- 

 racters. Nevertheless one does not see why the female 

 Brachyura furnished with Sacculince do not lose tlieir ovige- 

 rous feet which have become useless. 



3. The fact that in eases of infestation there is really no 

 manifestation of female characters in the male sex, or of male 

 characters in the female sex, leads us to attribute the modi- 

 fications of which we have been speaking to a simple arrest of 

 development of the external characters of the two sexes, an 

 arrest of development which is more noticeable in the male, 

 because in that sex the secondary sexual characters are, in the 

 normal state, much more developed than in the female. 

 * ' Beitrage zur Kenntniss der niauiilicher Cxeschlechtsorgane/ p. 83. 

 t Senckenb. Gos. natiirf. Freunde, 1870, p. 1. 



X Die von Ilerrn W. Peters iu " Mozaiubique gesammolten Cnista- 

 ceen," Moiiatsb. Akad. Berl. 1878, pp. 782-851. See also Tagbl. der 

 Versaimul. Deutsclier Naturf., Cast^el, 1878. 



