HORN KXPRDITION — NAKRATIVE. 127 



tin<:;uisli;iblo by tlie light line niong oitlior side of its body and tliougii iisn;dly 

 spoken of as the West Australian rock wallaby it is widely disti-ibiited over the 

 Centre, occurring on the Desert Sandstone ranges and throughout the (Jeorge (!ill, 

 Levi, James and McDonnell Ranges, in fact it is probably to be found amongst all 

 the hill country of the Central area. 



The average length of the body is two feet and the tail is just the same length 

 as the body. Three of the specimens were females and each of them had :i single 

 young one in the pouch, so that proli;ibly this may be rega,r<led ns the usual 

 nund)er produced at each birth. The young ones giow to a considerable! size 

 before leaving the pouch, and as the rock w;dlaby lives exclusively amongst the 

 hills, never apparently spending any time in the flats, a large nundjer of young 

 ones to be carriecl about at a time wouM be a serious handicap in a region where 

 birds f)f prey such as the wedge-tailed eagle are constantly on the look out 

 for food. 



The explanation of the way in which such an animal as the rat oi' the rabbit 

 if introduced into a region previously occupied by marsupials soon exiM'cils in 

 number the lower forms is probably chjsely connected with this manner of carrying 

 the young. 



In the first place, at an age when a, young marsupial at sight of flanger at 

 once flies to its mothei-'s pouch a young rat or ral)bit is taking cari^ of itself. If 

 a hawk or eagle catches the mother raljbit the young one is left or T/re iwrsa. Tn 

 the case of a marsupial the mother has to cany the young ones, and not oidy does 

 the extra weight prevent her gaining shelter but, if caught, both she and the 

 young ones are sacrificed. As sdready pointed out, a very slight dillerence in 

 speed will save or lose the animal its life. When hard presstxl a kangaroo will 

 throw the young out of the pouch so as to be able to travel faster. In fact this 

 habit of carrying the young one for so long in the pouch is a severe handicap foi' 

 a marsupial when it comes in contact with a rodent, for though they may not 

 compete with one another directly so far as theii- food supply is concei-ned — though 

 many of them do this — still they both have to avoid a common enemy in the 

 nature of birds of prey. In the c;ise of such smaller marsupials as, for example, 

 species of Hminthopsis in which the nutnber of young produced at a birth is from 

 eight to ten and there are at least two broods in each year it is a matter of 

 considerable! surpiise that they are not much moi-e numerous than they are. The 

 explanation is probably associated with the fact that there is a considerable length 

 of time during which not only does the capture of the motlier result in her 



