TB.E DESCENT OR OBIOIN OF MAN 217 



The possession by male mammals of functionally imper- 

 fect mammary organs is, in some respects, especially curi- 

 ous. The Monotremata have the proper milk-secreting 

 glands with orifices, but no nipples; and as these animals 

 stand at the very base of the mammalian series, it is prob- 

 able that the progenitors of the class also had milk- 

 secreting glands, but no nipples. T^is conclusion is sup- 

 ported by what is known of their manner of develop- 

 ment; for Professor Turner informs me, on the authority 

 of Kolliker and Langer, that in the embryo the mammary 

 glands can be distinctly traced before the nipples are in 

 the least visible; and the development of successive parts 

 in the individual generally represents and accords with 

 the development of successive beings in the same line of 

 descent. The Marsupials differ from the Monotremata by 

 possessing nipples; so that probably these organs were first 

 acquired by the Marsupials, after they had diverged from, 

 and risen above, the Monotremata, and were then trans- 

 mitted to the placental mammals."" 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 nour- 

 ished their young; and in the case of the Marsupials, that 

 both sexes carried their young in marsupial sacs. This will 

 not appear altogether improbable, if we reflect that the males 

 of existing syngnathous fishes receive the eggs of the females 



2' Prof. Gegenbaur has shown ("Jenaische Zeitsohrif t, " B. 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. 116. 



Descent — ^VoL. I. — 10 



