746 



SCmNGE. 



[N. S. Vol. IY. No. 99. 



Prof. Wilhelm Leche, of the University of 

 Stockholm, upon the teeth of living and ex- 

 tinct Lemurs, in which different conclu- 

 sions are reached. 



He sums up his results as follows : ' ' The 

 observations brought together in the pre- 

 ceding sections include a number of facts 

 which are of general significance and which 

 may be of general service. During the 

 Eocene and Oligocene periods, Europe and 

 North America were inhabited by groups of 

 Lemurs, which contained a number of 

 genera distributed in both hemispheres. 

 During the Oligocene every trace of these 

 Lemurs disappeared in the northern hemis- 

 phere, and we find no traces of these ani- 

 mals until they reappear among the exist- 

 ing forms of the Ethiopian and Indian re- 

 gions. To our complete ignorance of the 

 Lemurs during the long intermediate period 

 is added the fact that at first sight the 

 modern Lemurs appear to be a group widely 

 different genetically from those of Eocene 

 times. Yet, as I have endeavored to 

 demonstrate above, the difference between 

 the living and extinct Lemurs is by no 

 means so great as it is generally supposed 

 to be. Among the old Tertiary forms the 

 strong differentiation of the teeth in the 

 anterior portion of the jaw, which charac- 

 terizes the living forms, had not arisen. 

 Yet even in these older forms we see cer- 

 tain indications which point towards such 

 a differentiation. Notably supporting such 

 a conclusion are the discoveries in the milk 

 dentition of weight. 



" Until we obtain further knowledge, as 

 above stated, we must distinguish two 

 groups of extinct Lemurs, the most com- 

 plete representatives of which are Adapis 

 and Microchaerus.^ In spite of all the 

 differences between these two groups, there 

 are, nevertheless, exhibited a number of 

 common characters, in which they together 



*Prof . Lecbe considers Necrolemur Filhol. as equiva- 

 lent to this form. 



appear to present a more primitive consti- 

 tution than any of the living Lemurs. To 

 select a single illustration, among the older 

 tertiary Lemurs we still find four premolars 

 and three upper incisors, while in the living 

 forms we never find more than three pre- 

 molars and two upper incisors.* 



" Among the living forms we have cer- 

 tainly to distinguish two groups, the Lemur- 

 idce and Tarsiidce, the latter uniting most 

 closely with Microchoerus and its related 

 forms. Now, while the modern Tarsius, in im- 

 portant parts of its structure — in the struc- 

 ture of its placenta, in the structure of its 

 orbit and in the straight colon — certainly has 

 taken a different developmental direction 

 from the remaining Lemurs and deserves 

 an isolated position, nevertheless, its milk 

 dentition shows such a close approach to 

 thab of the true Lemurs that a common 

 derivation of the Lemuridce and Tarsiidce 

 must be considered as at least highly prob- 

 able. For the hypothesis which I have en- 

 deavored to establish in my earlier work, 

 that the milk teeth are to be regarded as the 

 representatives of an earlier developmental 

 phase, with more primitive characters than 

 the permanent teeth, we find that the teeth 

 of the Lemurs lend a number of supporting 

 features : First, in Hapalemur the superior 

 incisors have a more normal position in the 

 milk dentition than in the permanent denti- 

 tion. Second, the second upper premolar 

 of Adapis has retained the original pre- 

 molar form more completely than its per- 

 manent successor. Third, the lower in- 

 cisors of the Lemurs are somewhat less 

 modified than their successors. Fourth, 

 the second lower premolar of the Lemurs 

 has, as is well known, taken on the form of 

 a canine, while the milk tooth correspond- 

 ent to this retains the more ancient pre- 

 molar form. Fifth, in the Indrisince and in 

 Chiromys the milk dentition retains almost 



* Prof. Leche has evidently overlooked Anaptomor- 



