106 MR. W. BATESON ON [Feb. 2, 



The case of the great variability of the teeth of the large An- 

 thropoids, which is shown not merely in numerical changes, 

 but in frequent abnormalities of position and arrangement, is most 

 striking, both when it is compared with the great rarity of variations 

 in the teeth of the Old World Monkeys and the comparative 

 rarity of great variations even in Man. If the Seals or the 

 Anthropoids had happened to be domesticated animals, I do 

 not doubt that many persons would have seen in this variability 

 a consequence of domestication. When the whole evidence is 

 examined, it will be found that we can make no generalizations of 

 this kind, and that the variability of a form is, so far as can be seen, 

 as much a part of its specific characters as any other feature of its 

 organization. A few curious cases may be given in illustration. 

 Of Canis cancrivorus, a S. American Fox, I know the following 

 specimens only (in the British Museum) — normals (numerically) : 

 one whole skull with lower jaw, one skull without lower jaw, and 

 one lower jaw without a skull, and in one of these right m' is much 

 larger than the corresponding left tooth ; abnormals : two skulls 

 have ui^ on both sides, and a third has a large " odontome" formed 

 as 4 small molars growing from right m-^. Of Felis fontanieri, an 

 aberrant Leopard, two skulls only are known (British Museum), and 

 both of these show dental abnormalities, one having supernumerary 

 left m^, and the other having an additional talon to right p^, making 

 it almost a " bigeminous " tooth. In the Seals only three cases of 

 reduplication of the first premolar were seen, and two of these were 

 in Cijstophora cristaia (Leyden and Cambridge). Evidence of this 

 kind might be multiplied indefinitely. 



The following cases are chosen as representative examples or 

 "Prerogative Instances" of different classes of phenomena which 

 occur in connexion with increase in number of teeth. It will be 

 understood that the cases are selected as illustrations, and that in 

 order to have a full appreciation of their significance, the whole 

 body of evidence must be taken together, for scarcely any two cases 

 are exactly alike. 



Division of individual Teeth. 



Ommatophoca rossii. — Of this form two skulls only are known, 

 namely, those in the British Museum. One of them has the 

 arrangement usually found in Phocidse, viz., five teetli behind the 

 canines, giving the formula : — i. ^^, c. ^p p. + m. ?^. By the 

 analogy of other Seals, these five teeth are p. j, m. j. The other 



specimen is exceedingly remarkable (fig. 1). In it the incisors 

 and the canines are the same as in the first specimen, but the first 

 tooth behind the canine on both sides in the lower jaw and on the 

 right side in the upper jaw has a very peculiar form, having a deep 

 groove passing over the whole length of the tooth on both its outer 

 and inner sides. These grooves extend from the tip of the root 

 along both sides of the crown, and thus imperfectly divide each 

 tooth into an anterior and a posterior half. The cusp of each tooth 



