208 THE DESCENT OF MAN. Part I. 



difficulty. In the mammalian class the males possess 

 in their vesiculaa prostraticae rudiments of a uterus with 

 the adjacent passage ; they bear also rudiments of 

 mammae, and some male marsupials have rudiments 

 of a marsupial sack. 24 Other analogous facts could be 

 added. Are we, then, to suppose that some extremely 

 ancient mammal possessed organs proper to both sexes, 

 that is, continued androgynous after it had acquired 

 the chief distinctions of its proper class, and therefore 

 after it had diverged from the lower classes of the 

 vertebrate kingdom ? This seems improbable in the 

 highest degree; for had this been the case, we might 

 have expected that some few members of the two 

 lower classes, namely fishes 25 and amphibians, would 

 still have remained androgynous. We must, on the 

 contrary, believe that when the five vertebrate classes 

 diverged from their common progenitor the sexes 

 had already become separated. To account, however, 

 for male mammals possessing rudiments of the acces- 

 sory female organs, and for female mammals possessing 

 rudiments of the masculine organs, we need not suppose 

 that their early progenitors were still androgynous after 

 they had assumed their chief mammalian characters. 

 It is quite possible that as the one sex gradually 

 acquired the accessory organs proper to it, some of the 

 successive steps or modifications were transmitted to 

 the opposite sex. When we treat of sexual selection, 

 we shall meet w r ith innumerable instances of this form 

 of transmission, — as in the case of the spurs, plumes, 



24 The male Thylacinus offers the best instance. Owen, ' Anatomy 

 of Vertebrates,' vol. iii. p. 771. 



25 Serranus is well known often to be in an hermaphrodite condition ; 

 but Dr. Giinther informs me that he is convinced that this is not its 

 normal state. Descent from an ancient androgynous prototype would, 

 however, naturally favour end explain, to a certain extent, the recur- 

 rence of this condition in these fishes. 



