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 

 vol. i. p 



