296 MISCELLANEOUS OBJECTIONS TO THE [Chap. VIL 



a secretion from the cutaneous glands of the sack. Now 

 with the early progenitors of mammals, almost before 

 they deserved to be thus designated, is it not at least pos- 

 sible that the young might have been similarly nour- 

 ished? And in this case, the individuals which secreted 

 a fluid, in some degree or manner the most nutritious, so 

 as to partake of the nature of milk, would in the long 

 run have reared a larger number of well-nourished off- 

 spring, than would the individuals which secreted a 

 poorer fluid; and thus the cutaneous glands, which are 

 the homologues of the mammary glands, would have 

 been improved or rendered more effective. It accords 

 with the widely extended principle of specialisation, 

 that the glands over a certain space of the sack should 

 have become more highly developed than the remainder; 

 and they would then have formed a breast, but at first 

 without a nipple, as we see in the Ornithorhyncus, at the 

 base of the mammalian series. Through what agency 

 the glands over a certain space became more highly 

 specialised than the others, I will not pretend to decide, 

 whether in part through compensation of growth, the 

 effects of use, or of natural selection. 



The development of the mammary glands would have 

 been of no service, and could not have been effected 

 through natural selection, unless the young at the same 

 time were able to partake of the secretion. There is no 

 greater difficulty in understanding how young mam- 

 mals have instinctively learnt to suck the breast, than in 

 understanding how unhatched chickens have learnt to 

 break the egg-shell by tapping against it with their 

 specially adapted beaks; or how a few hours after leav- 

 ing the shell they have learnt to pick up grains of food. 

 In such cases the most probable solution seems to be, 



