in VARIABILITY OF SPECIES IX A STATE OF NATURE 49 



each specimen are then laid down in the same manner at 

 convenient distances apart for comparison ; and we see that 

 their variations bear no definite relation to those of the body, 

 and not much to those of each other. With the exception of 

 No. 5, in which all the parts agree in being large, there is a 

 marked independence of each part, shown by the lines often 

 curving in opposite directions ; which proves that in those 

 specimens one part is large while the other is small. The 

 actual amount of the variation is very great, ranging from 

 one-sixth of the mean length in the neck to considerably more 

 than a fourth in the hind leg, and this among only fourteen 

 examples which happen to be in a particular museum. 



To prove that this is not an isolated case, Professor Milne 

 Edwards also gives a table showing the amount of variation in 

 the museum specimens of six common species of lizards, also 

 taking the head as the standard, so that the comparative 

 variation of each part to the head is given. In the accompany- 

 ing diagram (Fig. 2) the variations are exhibited by means of 

 lines of varying length. It will be understood that, however 

 much the specimens varied in size, if they had kept the same 

 proportions, the variation line would have been in every case 

 reduced to a point, as in the neck of L. velox which exhibits 

 no variation. The different proportions of the variation lines 

 for each species may show a distinct mode of variation, or may 

 be merely due to the small and differing number of specimens ; 

 for it is certain that whatever amount of variation occurs 

 among a few specimens will be greatly increased when a much 

 larger number of specimens are examined. That the amount of 

 variation is large, may be seen by comparing it with the actual 

 length of the head (given below the diagram) which was used 

 as a standard in determining the variation, but which itself 

 seems not to have varied. 1 



Variation among Birds. 



Coming now to the class of Birds, we find much more 

 copious evidence of variation. This is due partly to the fact 

 that Ornithology has perhaps a larger body of devotees than 

 any other branch of natural history (except entomology) ; to 

 the moderate size of the majority of birds ; and to the circum- 

 1 Ann. des Sci. Nat., torn. xvi. p. 50. 



