Development of the Mammalian Phylum. 371 



lian pliylum, and renders it probable that tlie group had its 

 origin in the Palaeozoic period. In the examination of the 

 Triassic mammals we have to rely almost exclusively on the 

 teeth, the structure of which is extremely peculiar. It is 

 true that in many respects they still have a reptilian character, 

 whicli is especially visible in the small development of the 

 root ; but not only do we find a specialization of the den- 

 tition into incisors, canine, and molars, but the structure of 

 the latter is in the highest degree remarkable, for each molar 

 is composed of numerous cusps, which are arranged in two 

 or three rows and are separated by longitudinal furrows. 

 In consequence of this the name '' Multituberculata " has 

 been bestowed upon these ancient mammals. 



A year ago I advanced the theory that the molars of the 

 Mammalia are to he regarded as having arisen owing to the 

 fusing together into groups of original conical reptilian teeth*, 

 and this conception was chiefly derived from the observation 

 of the contrary process, since in whalebone whales a large 

 number of teeth with single tips is produced from original 

 multicuspid molars through fission, which sets in in the course 

 of the development. Now in the molars of the Multituber- 

 culata I find an important argument in favour of my view. 

 I regard a molar of one of these mammals as having arisen 

 through the fusion of a number of conical reptilian teeth, and, 

 simultaneously with this, a fusion of the corresponding 

 successional teeth with one another and the first series. In 

 the case of the multituberculate molars, which are provided 

 with three longitudinal rows of cusps, a fusion of corresponding 

 teeth of the third dentition is superadded. The fusion of 

 teeth belonging to successive dentitions is in itself in no way 

 wonderful. The difference in the time of appearance is indeed 

 an absolutely secondary phenomenon, and in the highest 



* This idea, which was suggested by me -with the necessary reserve, 

 was rejected as iufelicitous by O. Thomas (" Notes on Dr. W. Kiikenthars 

 Discoveries in Mammalian Dentition," Ann. i^- Mag. Nat. Ilist. ser. 6, 

 vol. ix. no. 52, p. 312), who, in doing so, relies chiefly upon the fact that 

 the number of teeth in the primitive IMammalia is greater than that 

 which ia found in many Anomodoutia, the most mammalian of the 

 Reptilia. " This fact is alone sufficient to discredit Dr. Kiikenthal's 

 theory." Although nosv as ever I am far from regarding my idea as a 

 thoroughly substantiated theory-, I would nevertheless here point out that 

 after what I have stated above'as to the position of the Theromorpha it 

 is impossible for me to admit this objection. In an essay which has 

 appeared during the printing of this paper (** Ueber die Entstehung der 

 Foruiabiinderuug der menschliclieu INlolaren," Anat. Anz. June '6, 1892) 

 Herr Kcise adopts my conception, and designates it as his theory, without 

 even mentioning mej although he is acquainted with my papers on this 

 subject. 



