200 THE DESCENT OF MAN. [Part I. 



the chief distinctions of its proper chxss, and therefore after 

 it liad diverged from the lower classes of the vertebrate 

 kingdom ? Tliis 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 " 

 and amphibians, would still have remained androgynous. 

 We must, on the contrary, believe that when the five ver- 

 tebrate classes diverged from their common progenitor the 

 sexes had already become separated. To account, how- 

 ever, for male mammals possessing rudiments of the accesso- 

 ry female organs, and for female mammals possessing rudi- 

 ments 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 possi- 

 ble that, as the one sex gi'adually acquired the accessory or- 

 gans proper to it, some of the successive steps or modili- 

 cations were transmitted to the opposite sex. When we 

 treat of sexual selection, we shall meet with innumerable 

 instances of this form of transmission — as in the case of 

 the spurs, plumes, and brilliant colors, acquired by male 

 birds for battle or ornament, and transferred to the fe- 

 males in an imperfect or rudimentary condition. 



The possession by male mammals of functionally im- 

 perfect mammary organs is, in some resjiects, especially 

 curious. Tlie Monotremata ha^•c the proper milk-secret- 

 ing glands with orifices, but no nipples ; and, as tiiese 

 animals stand at the very base of the mammalian series, 

 it is probable that the progenitors of the class possessed, 

 in like manner, the milk-secreting glands, but no nipples. 

 This conclusion is supported by what is known of their 



*' Serramis is well known often to be in an licrmaphrodite condition ; 

 Init Dr. Giinther informs me that he is convinced that this is not its nor- 

 mal state. Descent from an ancient androgynous prototype would, how- 

 ever, naturally favor and explain, to a certain extent, the recurrence of 

 this condition in these fishes. 



