46 DARWINISM chap. 



■wings, on which generic and family distinctions are often 

 established, are also subject to variation. The Eev. E. P. 

 Murray, in 1872, laid before the Entomological Society 

 examples of such A^ariation in six species of butterflies, and 

 other cases have been since described. The larvae of butter- 

 flies and moths are also very variable, and one observer 

 recorded in the Proceedings of the Entomological Society for 

 1870 no less than sixteen varieties of the caterpillar of the 

 bedstraw hawk-moth (Deilephela galii). 



Variation among Lizards. 



Passing on from the lower animals to the vertebrata, we 

 find more abundant and more definite evidence as to the 

 extent and amount of individual variation. I will first give a 

 case among the Eeptilia from some of Mr. Darwin's un- 

 published MSS., which have been kindly lent me by Mr. 

 Francis DarAAnn. 



"M. Milne Edwards (Annates des Sri. Nat, 1 ser., tom. 

 xvi. p. 50) has given a curious table of measurements of four- 

 teen specimens of Lacerta muralis ; and, taking the length of 

 the head as a standard, he finds the neck, trunk, tail, front 

 and hind legs, colour, and femoral pores, all varying wonder- 

 fully ; and so it is more or less "ndth other species. So ap- 

 parently trifling a character as the scales on the head affording 

 almost the only constant characters." 



As the table of measurements above referred to would give 

 no clear conception of the nature and amount of the variation 

 Avdthout a laborious study and comparison of the figures, I 

 have endeavoured to find a method of presenting the facts to 

 the eye, so that they may be easily grasped and appreciated. 

 In the diagi'am opposite, the comparative variations of the 

 different organs of this species are given by means of variously 

 bent lines. The head is represented by a straight line because 

 it presented (apparently) no variation. The body is next 

 given, the specimens being arranged in the order of their size 

 from No. 1, the smallest, to No. 14, the largest, the actual 

 lengths being laid doAATi from a base line at a suitable 

 distance below, in this case two inches below the centre, the 

 mean length of the body of the fourteen specimens being two 

 inches. The respective lengths of the neck, legs, and toe of 



