NATURAL SCIENCES OF PHILADELPHIA. 



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the table with reference to absolute length of tail-vertebras (with 

 which absolute length of feet is approximately correspondent) 

 show complete intermixture of localities. Measurements of a 

 hundred or a thousand specimens would of course only tend to 

 place these facts in stronger light. It may be safely stated as a 

 fact, then, that differences in absolute size, either of the body or 

 of any of its members, are not available for distinction of two 

 species; and furthermore, that no set of absolute dimensions is 

 correlated with geographical distribution. 



Nevertheless, one cannot fail to be struck, in examining the 

 table, with the extraordinary discrepancy in relative length of 

 the body and tail. In No. 48*71, for example, the tail (vertebrae) 

 is only half an inch longer than the head and body (4.50-5.00) ; 

 that is to say, it is but one-ninth of the head and body length 

 longer. In No. 2626 the tail is two and three-quarter inches 

 longer than the head and body ; that is to say, almost twice as 

 long. It would appear improbable that such unusual difference 

 as this should not signify something more than mere individual 

 variability. In order to discover whether or not the -proportion- 

 ate (as distinguished from absolute) dimensions of body and tail 

 may not lead to some tangible result, the following table is con- 

 structed, in which the same specimens are arranged geographically. 

 It is necessary to exclude four of them however (Nos. 9418, 1349), 

 from unknown localities, together with the two respectively marked 

 " California" and " Rocky Mts.," as I have reason to believe that 

 these indications of locality are not reliable. 



Measurements. 



