THE SERVICE OF TAILS 



75 



that it is enabled to make its long, running leaps, 

 which, in the case of the large wallaby, will aver- 

 age eight or ten yards at each jump. This is now 

 known to be largely an error ; the truth (as shown 

 by its tracks in the mud and by careful observa- 

 tion) is, that the tail only just touches the ground 

 now and then ; yet it is plain that this heavy mem- 

 ber serves a useful purpose in balancing the creat- 

 ure. The same must 

 have been true of those 

 vast reptiles of the 

 Mesozoic days, the 

 dinosaurs, whose 



rHE jERr.OA 



Kangaroo. 



tracks are 

 impressed so plen- 

 tifully upon the 

 brownstone rocks 

 of the Connecticut 

 valley, and of similar animals, in other parts of the 

 ancient world, known to have had enormous caudal 

 parts — a characteristic of primitive forms. 



One very distinct service the tail of one modern 

 marsupial may perform, is illustrated in the be- 

 havior of the jerboa kangaroo, which collects the 



