Chap. VI. 
AFFINITIES AND GENEALOGY. 
209 
an d 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 
^perfect mammary organs is, in some respects, espe- 
cially curious. The Monotremata have the proper milk- 
secreting glands with orifices, but no nipples; and as 
^ese 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 
hy what is known of their manner of development; 
Idr Professor Turner informs me, on the authority of 
Rulliker and Langer, that in the embryo the mammary 
glands can be distinctly traced before the nipples are 
m 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 beiugs in the same line of descent. 
.1 he Marsupials differ from the Monotremata by possess- 
ln g nipples; so that these organs wore probably first 
Required by the Marsupials after they had diverged 
lr °m, and risen above, the Monotremata, and were 
^cn transmitted to the placental mammals. No one 
"Hi 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 
’"’ere 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 
miperfect condition to the males. 
Nevertheless a suspicion has sometimes crossed my 
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