208 
THE DESCENT OF MAN. 
Part L 
difficulty. In the "mammalian class the males possess 
in their vesiculse prostration 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, v 7 e 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 w r ere 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, 
24 The male Thylacinus offers the best instance. Owen, ‘Anatomy 
of Vertebrates,’ vol. iii. p. 771. 
25 Serranns is well known often to be in an hermaphrodite condition • 
but Dr. Gunther informs me that he is convinced that this is not its 
normal state. Descent from an ancient androgynous prototype would, 
however, naturally favour and explain, to a certain extent, the recur- 
rence of this condition in these fishes. 
