228 MERISTIC VARIATION. [part i. 



towards the right upper canine. The whole anterior part of the lower 

 jaw is thus twisted a little towards the left side. 



Besides these two definite cases of absence of incisors, in the following instances 

 there was a presumption that the absence was due to variation, but a definite state- 

 ment cannot be made. 



H. smithii: only four incisors in lower jaw. B. M., 1435, a. H. gracilis: 

 doubtful case of absence of {i on both sides. B. M., 789, b. H. nyula : doubtful if 

 right f has been present. B. M. 



Anterior Premolars. 



In the great majority of both Asiatic and African species of Her- 

 pestes the anterior premolar (p l ) is normally present in both jaws, and 

 in these species 6 cases of absent p- were seen. When present it 

 is a tooth of small but still considerable size. It appeared from 

 the specimens that ^ in the species H. gracilis (Africa generally), 

 and both l^_ and y in H. galera (E. Africa) are commonly absent. As 

 in other cases of absence of teeth the question arises whether the 

 absence is due to age or accident, or on the other hand to original 

 deficiency. This question cannot be definitely answered, but some 

 considerations touching it should be mentioned. 



First, as has been said, the tooth when present is of moderate size: 

 though small, it is quite large enough to be functional, and is in no 

 sense rudimentary. In his synopsis of the genera, Thomas 1 says of 

 Herpestes, " Premolars |- (if only 3 in either jaw, a diastema always 

 present)." There is however no reason for supposing that the presence 

 or absence of p l is determined by chance. From the fact that a tooth 

 is small, it by no means follows that it is often lost. To any one 

 handling large numbers of skulls, instances of the contrary must be 

 familiar. A case in the Otters well illustrates this point. In Lutra 

 vulgaris upper ]? is a small tooth, and from its singular position internal 

 to the canine, it might be supposed that the development of the canine 

 might easily push it out; yet in 41 skulls of Lutra vulgaris, only 

 1 case of absence of P^ was seen. Of L. cinerea on the contrary six 

 skulls are without p] ; but as in two young skulls it is present on 

 both sides, there is thus a strong presumption that in this species the 

 tooth is lost with maturity. The frequent absence in the one species 

 and the constant presence in the others points to a difference in 

 organization between them. When p l is missing in a skull, though we 

 are not entitled to infer that it has not been present, still the fact of 

 its presence in one case and of its absence in another is on the face of 

 it an indication that between the two there is a difference or Variation, 

 but whether the Variation lay in the number of teeth originally 

 formed or in the mode in which they were affected by subsequent growth 

 is uncertain. In the specimens to be described the absence of p 1 in 

 certain individuals or species is no less definite than its presence in the 

 others, and that which is a variation in one species will be seen to be 

 the rule in others. 



As regards the presence of p l the specimens thus make a pi'ogressive 

 series. Most species having^, but p^ as a variation; H. gracilis (and 



pulverulentus) having p~ normally, but p\ as a variation and p- „ 



o — o 



1 Thomas, 0., on the African Mungooses, P. Z. S., 1882, p. 62. 



