Chap. VI. 
AFFINITIES AND GENEALOGY. 
209 
and brilliant colours, acquired by male birds for battle 
or ornament, and transferred to the females in an im- 
perfect or rudimentary condition. 
The possession by male mammals of functionally 
imperfect mammary organs is, in some respects, espe- 
cially curious. The Monotremata have the proper milk- 
secreting glands with orifices, but no nipples; and as 
these animals stand at the very base of the mam- 
malian 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 manner of development ; 
for Professor Turner informs me, on the authority of 
Kolliker and Lauger, that in the embryo the mammary 
glands can be distinctly traced before the nipples are 
in the least visible ; and it should be borne in mind that 
the development of successive parts in the individual 
generally seems to represent and accord with the deve- 
lopment of successive beings in the same line of descent. 
The Marsupials differ from the Monotremata by possess- 
ing nipples; so that these organs were probably first 
acquired by the Marsupials after they had diverged 
from, and risen above, the Monotremata, and were 
then transmitted to the placental mammals. No one 
will suppose that after the Marsupials had approxi- 
mately acquired their present structure, and therefore 
at a rather late period in the development of the 
mammalian series, any of its members still remained 
androgynous. We seem, therefore, compelled to recur 
to the foregoing view, and to conclude that the nipples 
were first developed in the females of some very early 
marsupial form, and were then, in accordance with a 
common law of inheritance, transferred in a functionally 
imperfect condition to the males. 
Nevertheless a suspicion has sometimes crossed my 
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