-7 '2 M ERISTIC VARIATION. [PART i. 



Variation of unusual amplitude may be seen also in the molars 

 df lii-tttni<ini No-.. .'>vi, &c., for while on the one hand the last or 

 fourth mi ilar may In- absent, it may on the contrary be large and 

 mav even l)i- succeeded by a fifth molar as an extra tooth. All 

 i lies,- conditions were seen in looking over quite a small number 

 <f -pel-miens. 



( 7 ) Il"/noeotic Variation in terminal Teeth ivlien a new member 



is milled bt'liinil thnn. 



(']><>n tin- remarks made in the last Section the fact here 

 M. .tired naturally follow-. We have seen that there is a fairly 

 constant relation between the size of extra teeth and that of the 

 teeth next t> which they stand, so that the new teeth are as it 

 w.re, from the first, of a size and development suitable to their 

 position. We have now to notice also that the teeth next to which 

 the\- stand ma\ al-o undergo a variation in correlation with the 

 presence of a new tooth behind them. 



It may be stated generally that if the tooth which is the last 

 ..f a normal series is relatively a small tooth, as for example m? or 

 "- in the Dog, then in cases of an addition to the series, by which 

 this terminal tooth becomes the penultimate, it will often (though 

 not always) be found that this penultimate tooth is larger and 

 I" M.I developed than the corresponding ultimate tooth of a normal 

 animal of the same size. 



Of this phenomenon two striking examples (q. v.) have been 

 given, ('(mix azane No. 249 and Dasyurns maculatus No. 385. 

 I '.. sides these are several others of a less extreme kind e.g. Otocyon 

 meyalotis No. 250, Mastiff No. 259, Dog No. 260. The same was 

 also seen in the molars of Bettongia. 



This phenomenon, of the enlargement of the terminal member 

 of a series when it becomes the penultimate, is not by any means 

 confined to teeth ; for the same is true in the case of ribs, digits, 

 &c., and it is perhaps a regular property of the Variation of Meristic 

 Series s.. graduated that the terminal member is comparatively 

 .-mall. This fact will be found of great importance in any attempt 

 to realize the physical process of the formation of Meristic Series, 

 and it may be remarked that such a fact brings out the truth that 

 the members of the Series are bound together into one common 

 u hole, that the addition of a member to the series may be cor- 

 related with a change in the other members so that the general 

 configuration of the whole series may be preserved. In this case 

 the new member of the series seems, as it were, to have been 

 reckoned for in the original constitution of the series. 



(8) Reconstit^on of "parts of the Series. 



Lastly there are a few cases, rare no doubt in higher forms but 

 not \ery uncommon for example in the Sharks and Rays (see 



