ig6 PRIMARY FACTORS OF ORGANIC EVOLUTION. 



perior incisor teeth, rudiments of them can be found 

 in the early stages. We now know early extinct forms 

 of both of these types where these teeth are permanent 

 throughout life. In the toothless whalebone whales 

 the same phenomenon has been observed. 



It is well known that the highest deer (Cervidae) 

 add an antler to the simple spike horn in the third 

 year, and an additional antler with each successive 

 year for several years. Also they develop a basal snag 

 of the antler (see Cuvier, Ossem. Fossiles ; Gray, Catal. 

 Brit. Mus.} at the third year. Now a majority of those 

 of the New World (genera Cariacus, Coassus) never 

 develop it except in "abnormal" cases in the most 

 vigorous maturity of the most northern Cariacus (C. 

 virginianusy, while the South American Coassus retains 

 to adult age the simple horn of the second year of 

 Cervus. 



Among the higher Cervidae, Rusa and Axis never 

 assume characters beyond an equivalent of the fourth 

 year of Cervus. In Dama the characters are on the 

 other hand assumed more rapidly than in Cervus, its 

 third year corresponding to the fourth of the latter, 

 and the development in after years of a broad plate' of 

 bone, with points, being substituted for the addition 

 ot the corresponding snags, thus commencing another 

 series. 



Returning to the American deer, we have Blasto- 

 cerus, whose antlers are identical with those of the 

 fourth year of Cariacus. 



The oldest known deer (Palseomeryx) have no 

 horns, or they are undivided. 



Among Batrachia excellent illustrations are fur- 

 nished by the two series of Salientia, the Arcifera and 

 the Firmisternia. 



