198 M ERISTIC VARIATION. [PART I. 



Pike, the Alligator, or the Toothed Whales, for example, the teeth 

 I in ,i P -pillar and usually continuous series, differing from 

 ad, other chiefly in size, ranging from small teeth in from, 

 through large teeth, and often down to small teeth again ai the 

 1 a.-k ' .f t h.- jaw. Such a 'homodont' series as a rule passes through 

 ,,nlv one ni'axinium. Most mammals, however, are 'heterodont,' 

 iha't LB to say, the teeth can be distinguished into at least two 

 groups, ih' incisors and canines on the one hand, and the pre- 

 molarfi and molars on the other; and in a large number of animal- 

 having tin- arrangement the anterior members of the series ot 

 premolars and molars are small, increasing regularly in size from 

 before l.a-k\\ards, reaching a maximum usually in some tooth 

 anterior to th.- last. Though instances will be given of Variation, 

 and especially "f reduplication, occurring in most of the teeth, 

 even in those which stand well in the middle of the series of back- 

 h. auch as tin upper carnassials of the Cat, or the fourth pre- 

 molai-; of ill, Seal, ye\ on the whole Variation in heterodont forms 

 i-, more common at tin- anterior and posterior ends of the series of 

 back -teeth. In view of this fact it is of some importance to 

 recognize that th<- -mall members at the beginning of the pre- 

 molai- series are as n -gards their relatively small size, in the con- 

 dition of terminal memb.-rs of series, and exhibit the variability of 

 ti -rniinal memb.-ix almost as much as the last molars. 



With these n-niarks by way of preface, evidence as to the 

 num. -i-ical \'ariatiou of teeth in certain groups will be given in full. 

 Thi- account will lor the most part be confined to a brief description 

 of the conditions piv-mted by the specimens. In the next chapter 

 the principles which may be perceived to underlie these facts and 

 the general conclusions to which they appear to lead will be 

 -parately discussed. 



The evidence here given relates to certain selected groups 1 of 

 Mammal-, ami chiefly to the lYimate-, (excepting Lemuroidea), Car- 

 nivora i( 'anida-, Felida-, Yiverrida-, Mustelidae and Pinnipediae), and 

 Marsupialia I 1'halangerida', 1 )a>yiirida- t I)idelphyidai, part of Macro- 

 podida-. >Vc.). 



The tacts to be given relate chiefly to increase in number 

 of teeth. In the case of terminal members of series, such as the 

 moM anterior pivmolar or the last molar, some reliable facts as to 

 i-asi - of alr-^nce \\.-re found, but )oi- the most part the evidence as 

 to the absence of teeth is ambiguous and each case requires 

 -parate treatment. 



The e\idence is in this chapter arranged according to the 



1 K\id. ];', as to tin- ilriitul variations of .Man is not hnv introduced. Con- 

 iiilili- o>lliTti>ns ft' siK'li diets have li.'cii niailf liy MAUITOT (Amnii. <lu ni/st. 



lint i. I'.i IOB (I>'Ht. Mi-iint.1. f. /.ahull. I.VMI. i\.i, and others, and illustrative 

 re i" ! found in most ninsriim-. I do not know that among these 



liiimiin variations air indinl. .1 piniiomeua dil'tVi.'iit in kind from those seen in 



otliiT K-roii]' . : I'.ilia]- i-.'i-tain eas.-s oi t-rth nnit.'l i ., , ther, a condition 



rarely if I-VLT recorded in other animals. 



