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chief cause of their sufferings and danger. During the dry 

 season the rivers are converted into pools, l few and far be- 

 tween ;' and the drought is sometimes continued so long as to 

 dry up these. An ordinary non-marsupial quadruped, such 

 as the wild cat or fox, having deposited her young in the nest 

 or burrow, would in such a climate, at the droughtiest period 

 of her existence, be compelled to travel a hundred, perhaps 

 two hundred miles, in order to quench her thirst. Before she 

 could return her blind and helpless litter would have perished. 

 By the marsupial modification the mother is enabled to carry 

 her offspring with her in the long migrations necessitated by 

 the scarcity of water. 



With the climatal peculiarities of Australia, therefore, we 

 may connect the peculiar modifications of those members of 

 the mammalian class which are most widely distributed over 

 that continent. But the principle of final causes receives more 

 especial illustrations from the contingent particulars of the 

 marsupial organization. The new-born Kangaroo is an inch 

 in length, naked, blind, with very rudimental limbs and tail : 

 .in one which I examined the morning after the birth, I could 

 discern no act of sucking : it hung, like a germ, from the end 

 of the long nipple, and seemed unable to draw sustenance 

 therefrom by its own efforts. The mother, accordingly, is 

 provided with a peculiar adaptation of a muscle (cremaster) to 

 the mammary gland, by which she can inject the milk from 

 the nipple into the mouth of the pendulous embryo. Were 

 the larynx of the little creature like that of the parent, the 

 milk might probably would enter the windpipe and cause 

 suffocation : but the foetal larynx is cone-shaped, with the 

 opening at the apex, which projects, as in the whale-tribe, 

 into the back aperture of the nostrils, where it is closely em- 

 braced by the muscles of the ' soft palate.' The air-passage 

 is thus completely separated from the fauces, and the injected 

 milk passes in a divided stream on either side the base of 

 the larynx into the oesophagus. These correlated modifica- 

 tions of maternal and foetal structures, designed with especial 



