68 THE EVOLUTION OF SEX. 



a merely superficial abnormality or even injury of the ducts in one sex 

 produces a resemblance to those of the other. 



We have already mentioned that in the case of twin calves, two females 

 may occur, and both are then normal ; or two normal twin calves may be 

 born of opposite sexes ; but in the third place, if both be males, one of 

 these very generally exhibits the peculiar phenomena of what is called a 

 "free-martin." In the commonest form of this, partial hermaphroditism 

 is well illustrated. The essential organs are male, but there is a rudiment- 

 ary uterus and vagina, and the external organs are further those of a female. 



It is'necessary to note, that a simulation of even this partial hermaphro- 

 ditism may result from malformation or rudimentary development of the 

 external organs. On this subject we may quote an acknowledged authority, 

 alike in anatomical and embryological matters. " From the fact," Prof. 

 O. Hertwig remarks, " that the external sexual organs are originally of 

 uniform structure in the two sexes, we can understand the fact that, in a dis- 

 turbance of the normal development, forms arise in which it is extremely diffi- 

 cult to decide whether we have to deal with male or female external organs. 

 These cases, in earlier times, were falsely interpreted as hermaphroditism. 

 They may have a double origin. Either they are referable to the fact that 

 in the female sex the development may proceed along the same path as in 

 the male, or to this, that in the male the normal development may come at 

 an early stage to a standstill, and lead to the formation of structures which 

 resemble the female parts." In the first case, he goes on to say, there may 

 be a simulation of a penis, and the ovaries may even be shifted so as to 

 produce an appearance like that of the testes within their scrotal sac. In 

 the second case, the processes of coalescence which give rise to the penis 

 may not occur, only a rudimentary organ is formed, and there may even be 

 an inhibition of the usual descent of the testes into their sacs. 



Of this superficial hermaphroditism, really not hermaphroditism at all, 

 there are numerous cases among mammals. But there remain a large 

 number of recorded instances, where the anatomy of the ducts was predomi- 

 nantly that of the sex opposite to that indicated by the essential organs, 

 and where the combination of the two sexes was also expressed in external 

 configuration and even in habit. Amphibians again furnish some inter- 

 esting examples. Attached to the anterior end of the testis in various 

 species of toad [Biifo), there is an organ known as " Bidder's," which has 

 contents like young ova. These do not, however, get past the early stages, 

 and the organ is quite different from the more than rudimentary ovary 

 which occurs constantly in the males of Biifo ciiiereiis and some other 

 species. The two may in fact occur together. In the common frog, 

 dissectors have also recorded several cases of hermaphroditism expressed in 

 the ducts. Lastly, it is perhaps not going too far to include here some 

 reference to the curious "fatty bodies" which occur in all amphibians at 

 the apex of the reproductive organs in both sexes. These appear to nourish 

 the ovary and testis, esi:)ecially during hybernation, and may perhaps be 

 associated with similar lymphoid structures in fishes and reptiles. Prof. 

 Milnes Marshall was of opinion that the fatty bodies have resulted from 

 the degeneration of the anterior part of the reproductive gland while still 

 in an indifferent state ; but Mr Giles has recently traced the history of these 

 bodies, and shown them to result from the degeneration of the anterior set 

 of excretory tubules, the pronephros. 



Leaving the ducts out of account, we may arrange the 



