200 THE DESCENT OF MAN. [Part L 



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 24 

 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 gradually acquired the accessory or- 

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

 cations were transmitted to the opposite sex. When we 

 treat of sexual selection, we shall meet with innumerable 

 instances of tnis 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 in> 

 perfect mammary organs is, in some respects, especially 

 curious. The Monotremata have the proper milk-secret- 

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

 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 . 



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

 but Dr. Giinther infoqjns me that he is convinced that this is not its nor- 

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

 c^er, naturally favor and explain, to a certain extent, the recurrence of 

 this condition in these fishes. 



