296 MISCELLANEOUS OBJECTIONS TO THE [Chap. VII. 



reared a larger number of well-nourished offspring, 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 ex- 

 tended 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 Ornithorhvncus, 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 mammals 

 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 

 Leaving the shell they have learnt to pick up grains of 

 food. In such cases the most probable solution seems 

 to be, that the habit was at first acquired by practice at 

 a more advanced age, and afterwards transmitted to the 

 offspring at an earlier age. But the young kangaroo is 

 said not to suck, only to cling to the nipple of its 

 mother, who has the power of injecting milk into the 

 niuuth of her helpless, half-formed offspring. On this 

 head Mr. Mivart remarks : " Did no special provision 



