140 STUDIES IN THE EVOLUTION OF ANIMALS 



back and light-coloured rump being very sharp. It might mean 

 that the ancestors of those ruminants had that rump shield, and 

 that it was got rid of earlier than the dorsal carapace, and thus a 

 sharp contrast of coloration was inherited in consequence. There 

 is an alternative supposition, for in some Armadillos we find that 

 the carapace stops short of the tail, and leaves a bare space 

 between the tail and posterior margin of the carapace, and this 

 fact may remain recorded in the ruminants and others that have a 

 white patch behind. It would seem to mean only a continuation 

 of the unarmoured ventral surface. 



Among the animals that are so patched behind are the 

 .Siberian Roebuck (Capreolus pygargus), Wapiti Deer (Cerviis 

 Canadensis), Pronghorn (Antilocapra Americana], Bonte-bok 

 (Dainalis pygargd], Sable Antelope (Hippotragus niger\ Scemmer- 

 ing's Antelope, and several others. It may be quite true that 

 animals now make use of these white patches as ' danger marks,' 

 and ' recognition marks,' but their origin is I think explained 

 by the abruptly truncated dorsal armour of some ancestral form. 

 In the 'Pichiciago' Armadillo of Argentina, the vacant space 

 is covered by an additional rump-shield, but in others it might be 

 absent, as we indeed see it in several other varieties of Armadillo. 



In this connection I would mention that in the Natural History 

 Museum there is an interesting and very suggestive preparation 

 of this little Armadillo. It has no calcareous or bony carapace 

 but only the epidermic horny shell of one. Under this horny shell 

 there is a hairy coat as in other animals. The curious part is, that 

 the horny shell is attached to the true skin by means of a thin 

 ligament all along the spine. This latter feature may perhaps 

 give us a clew to the interpretation of that spinal dark or white 1 



1 The Kerry breed of cattle are black, with a white streak down the back, and 

 sometimes another along the belly. (Roy. Nat. Hist.) vol. ii. p. 168. ) 



