The Rodent ia in Evolution. 51 



them been thus changed in habit much longer than others, 

 some being more competely correlated in their structure by 

 their peculiar habits than are others. 



The fourth suborder or Lagomorpha is very small and 

 contains only two genera, Lagomys and Lepus. These unite 

 in certain osteological characters unique among rodents, 

 especiallj^ : — 2 incisons on each side of the upper jaw (one 

 rudimentary.) This is a more simple condition than that of 

 remaining rodents and more nearly ancestral, reduction in 

 the number of the teeth being among the results of specializ- 

 ation in many cases (eg Ruminants Cetaceans, etc., and also 

 in the more specialized rodents.) The fibula, however, is not 

 distinct but is perfectly fused with the tibia, more com- 

 pletely than m any Myomorph so that in this respect the 

 Lagomorphs are more specialized than the Sciuromorphs. 

 The Pika and hares, burrowing terrestrial and leaping in 

 habit make up the suborder. 



It will appear from this summary that the rodents can- 

 not be classed by similarity of habit because if we were to 

 attempt to place together all the aquatic kind we should 

 have as a result a motley assembly of Sciuro, Historico and 

 Myomorphs alike only in a few superficial features but fund- 

 amentally wholly diverse. So too, if we should attempt to 

 put together all the fossorial rodents we should be obliged 

 to associate marmots, chinchilla and mice, separating these 

 essentially unlike creatures from arboreal terrestrial and 

 aquatic animals, totally difterent in habit which are in many 

 cases almost absolutely identical in bodily structure. Such 

 a procedure is intolerable to the scientist of today. It was 

 natural enough to the infantile scientist at the dawn of 

 science to call all aquatic animals fish, and the names star- 

 fish, etc., are survivals of this ancient tendency. But science 

 long since abandoded such crudities and habit and station 

 are inevitably regarded as the latest acquisitions of animals 

 to be followed later if it have any further history by struc- 

 tural adaptations to fit. 



Before passing to the fuller development of this last point, 

 I wish to dwell for a moment upon a detailed comparison of 

 the muskrat and the beaver, two aquatic rodents. The 

 dorsal surfaces of the skulls of these are represented in 



