262 Scientific Proceedings, Royal Dublin Society. 



application involves, has conferred a great boon upon those investigating late 

 Tertiary history, since it supplies us with a very powerful means of testing 

 such generalizations as that outlined in the preceding paragraph. It has 

 long been recognized that, as any given mammalian group moves outward 

 from its centre of dispersion, it suffers more or less profound modifications of 

 structure, so that the most highly specialized forms are in general precisely 

 those which exist, or have existed, furthest from the original centre of 

 dispersion. Good instances of this principle are afforded by tlie cervine 

 ruminants, where we find such transformations of the primitive type as the 

 G-irafPe, the Elk, and the Reindeer as peripheral representatives.' I hope to 

 show that exactly the same principle asserts itself in the case of the subspecies 

 of the L. rariahilis group. 



The Hares present us with a curious combination of ancient and modern 

 characters. The dental formula is very primitive compared with that of 

 other rodents; but the individual clieek -teeth have undergone the most 

 profound specialization. The organs of sight and hearing are greatly 

 enlarged ; and the limb-skeleton is well on its way to the reduced condition of 

 the swift-footed ungulates. Of the two groups of Hares with which we have 

 been concerned in this paper, viz., the mriabilis and eiiropceus groups, the 

 former is on the whole the more specialized. It is necessary for our 

 present purpose to look at the various members of the mriabilis group a 

 little in detail. 



Dealing first with the skull, Winge has shown us how to interpret the 

 changes found in proceeding from one member of the group to another. 

 We will confine our attention to the relations subsisting between the eye and 

 the ear, because tlie evidence of the fossil form and of Z. v. hibernicus on this 

 point also has a geological bearing. Both organs are abnormally large in 

 all Hares. With regard to the variabilis group, as we proceed northwards to 

 colder climes, the peripheral parts tend to diminish in size, not because tliey 

 are less useful to the animal, but because of the cold. In accordance with 

 this, the outer ear becomes shorter in the northern forms of the group ; but, as 

 Winge points out, the loss in this respect is compensated by an increase in 

 the size of the eye ; and this increase has its due eilect upon the skull, for as 

 the eye becomes larger the superciliary processes of the frontal tend to elevate 

 themselves more and more in proportion.^ In perfect harmony with this we 

 find that in L. v. hibernicus and in L. v. anglicus the superciliary processes are 

 less elevated and the interorbital region flatter than in any other forms of 



' EuTiMEyER, Beitrdge zu der Geschichte der Sirsclifamilie \. Schiidelbau. Verliand. der 

 Naturforsch. Gesell. in Basel, vii. Theil, 1. Heft, 1882, pp. 45-57. 

 ^ Winge, " Gronlands Pattedyr," p. 358, and " Pattedyr," p. 58. 



