364 W. B. Scott — Variations and Mutations. 



The study of the mammalian phyla brings out a number of 

 facts which I have elsewhere* endeavored to set forth and 

 which do not at all agree with those inferences drawn by 

 Bateson from an examination of the individual variations of 

 existing mammals. One is greatly tempted to conclude that 

 the two orders of facts are not, so to speak, commensurable. 

 Thus, Bateson hesitates to attribute to any one the explicit 

 maintenance of the thesis already quoted, namely, " that a 

 series [of parts or organs] consisted ancestrally of some maxi- 

 mum number, from which the formula characteristic of each 

 descendant has been derived by gradual diminution. Here, 

 again, I do not doubt that many who employ this assumption 

 would hesitate to make it in set terms, but nevertheless it is 

 the logical basis of all such calculations." The mammalian 

 paleontologist, however, need not hesitate to adopt this thesis, 

 not as an assumption, but as an inference from many facts and 

 to defend it with a great array of evidence, though always 

 remembering that nature declines to submit to our rigid sys- 

 tems and in such matters will make exceptions to modes of pro- 

 cedure which are, on the whole, remarkably constant. Thus, 

 there can be very little doubt that the numerous uniform teeth 

 of .the toothed whales are not primitively simple forms inheri- 

 ted from reptilian ancestors, but as Zettglodon indicates, the 

 dentition has been simplified and greatly increased in numbers 

 since the differentiation of the order. It would be a fruitless 

 task to attempt to homologize any of the teeth of Delphinus 

 with those of Zeuglodon. Kiikenthal has suggested with much 

 probability that the numerous teeth of certain edentate genera 



(20— 25\ 

 ^1 have been derived from the subdivision of complex 



molars of the glyptodont type. These facts, so far as they go, 

 agree with Bateson's conclusions, but then it should not be for- 

 gotten that they are very exceptional. Among heterodont 

 placental mammals there is but one case known as to which it 

 can be maintained with any show of probability that it has 

 developed an additional tooth, and that is Otocyon. Though, 

 for reasons which cannot be discussed here, I believe the 

 fourth molar of Otocyon to have been added since the separa- 

 tion of the canine phylum, we cannot attribute much weight 

 to this case until the history of the genus has been determined, 

 for it is quite within the bounds of possibility that this form 

 has retained the marsupial formula, not reacquired it. This is 

 the view held by most writers on the subject. The vast 



* On the Osteology of Poebrotherium, Journal of Morphology, vol. v, pp. 1-78. 

 On the Osteology of Mesohippus and Leptomeryx, Ibid., pp. 301-406. 

 The Mammalia of the Deep River Beds, Trans. Am. Phil. Soc, vol. xvii, pp. 

 55-185. 



