< MAI'TKK II! 



LINEAR SERIES continued. 

 VERTEBR/E AND RIBS. 



'I'm: Men-tic Vai-iati..us of the vertebral column constitute a 

 jed ..I some complexity. In considering them it must be 

 remembered that numerical change may be brought about in the 

 of vertebrae by \\\ different processes: first, by Variation in 

 tin- total Qumber of segments composing the whole column, in which 

 the variation i- truly Men-tic ; and second 1\ by Variation in 

 tin- number or ordinal position of tin- vertebra* comprised in one 

 or mop- regions of tin- column, not neces-arily involving change in 

 th- total number of segments forming the whole series, and in this 

 the \ariation i- Homo-otic. Though Eomceotic Variation is 

 often a-.-oriated \\ith change in the total number of segments, 

 fi-oni tin- natmv of the case it is rarely possible in any given 

 in-tanec to di>tinguish clearly whether >udi change has occurred 

 or DOt. Thi- ari-es largely from the tad 1 hat while to find the 



il numbet of vertebrae it is necessary to kn<>\\ the exact number 

 of caudal \ei-tebr;i', in man\ specimens the>e arc incomplete, and 



i if present their number cannot often be ^iven with con- 

 fideiice. For then reasons the chief interest of this section of the 

 fart- arises in connexion with Honiu-otic Variation, and the modes 

 in \\hich it OCCUTS; but it must be constantly borne in mind that 

 in almost ; my gi\en case there may be Mcristic Variation also, though 



the e\idelice of this lliaV be ob-CUl'ed. 



TlMI Ml Ills-Mi \'A];i.\TH'N IN \ I 1:11 Pi:. 1. ANI> iJlHS. 



I. V> iii /'fn . 



True M eristic \'ariation, that is to >,-i\. change in the total 

 number of .- u r "n m- conii-o-inL; the \\hole column. ma\ neverthe- 



le-s be j.lainly iec,, U Mii/ed in <-, itain animal-. Among -oine of the 



