The Descent of Man

mitted to the placental mammals. (29. Prof.
Gegenbaur has shewn ('Jenaische Zeitschrift,'
Bd. vii. p. 212) that two distinct types of nipples
prevail throughout the several mammalian
orders, but that it is quite intelligible how both
could have been derived from the nipples of
the Marsupials, and the latter from those of the
Monotremata. See, also, a memoir by Dr. Max
Huss, on the mammary glands, ibid. B. viii. p.
176.) No one will suppose that the marsupials
still remained androgynous, after they had approximately
acquired their present structure.
How then are we to account for male mammals
possessing mammae? It is possible that they
were first developed in the females and then
transferred to the males, but from what follows
this is hardly probable.
It may be suggested, as another view, that long
after the progenitors of the whole mammalian
class had ceased to be androgynous, both sexes
yielded milk, and thus nourished their young;