276 THE DENTAL SYSTEM OF THE PRIMATES [SECT. A 



he distinguishes by Roman numerals I — IV), the several elements 

 develop as follows : 



No. I. The teeth do not attain the stage of calcification, and 

 are represented by vestigial buds only, situated upon the labial 

 margin of the gum. 



No. II is regarded as the ordinary " milk " dentition. 



No. Ill is the ordinary permanent dentition. 



No. IV. This series is usually represented by " buds " on the 

 lingual side of No. Ill : these elements may sometimes arrive at 

 maturity and appear as definite teeth. Subsequently (in the 

 same memoir) Leche discusses the subject of the reduction in the 

 number of functional dentitions. He suggests that the reduction 

 was necessitated by the circumstances under which the mammalia 

 were evolved from pre-mammalian reptilian ancestors ; that how- 

 ever, only dentitions I and II have been inherited from such 

 ancestors, III and IV being newly evolved and peculiar to the 

 mammalia. This position is not quite easy to grasp in view of 

 the fact cited by Beddard (Mammalia, p. 53), that Leche has 

 himself described in a reptile (Iguana), no less than four series of 

 teeth which reach maturity, while a rudimentary (or vestigial) 

 series, antecedent to these, never produces fully formed teeth. 



But in the memoir quoted, Leche defends his position that 

 new dentitions can arise, though he recognizes the objections that 

 have been adduced by Kowalevsky, Schmidt, and Schlosser. 

 Finally, in a more recent memoir (Bibliotheca zoologica, Heft 37, 

 1902) upon the dentition of the Insectivora, Leche brings forward 

 further evidence in support of the foregoing view. 



These discoveries of a number of dentitions, some of which are 

 recognizable in the Hominidae, detract to some extent from the 

 value of Schwalbe's review of the subject as presented to the 

 German Anatomical Society in 1893. Nevertheless that address 

 still retains all its historical interest, and includes certain remarks 

 which may here be briefly recapitulated. In the first place, 

 Schwalbe points out the difficulty in determining criteria for the 

 several series of teeth. He quotes Leche as pessimistically ad- 

 mitting that such criteria are not to be hoped for, though the 

 same author clearly indicates that he regards each dentition as a 



