96 THE LESSON OF EVOLUTION 



At Glenmark the greatest number of tibiae are 

 eighteen and a half inches in length, with marked 

 negative, definite variation. But at Kapua the 

 average length had increased to nineteen inches,, 

 although still shewing negative definite variation. 

 In spite of this, the average length of the bone was 

 still greater at Enfield than at Kapua, but it now 

 shews indefinite variation. 



The femur at Glenmark is from ten and a half 

 to eleven inches in length, with hardly any varia- 

 tion. At Kapua it is larger, and shews more 

 variation, but the majority of these are on the nega- 

 tive side. Nevertheless, at Enfield the bone is still 

 larger, eleven to eleven and a half inches, w r ith a 

 majority of negative variations. 



Thus we see that Syornis casuarinus became 

 larger, especially in the tibia and femur, from 

 Glenmark to Kapua, and from Kapua to Enfield; 

 although in one case only the metatarsi at Glen- 

 mark do we find definite variation pointing in that 

 direction. There are five cases in which negative 

 definite variation was followed by increase in size. 

 At the same time there is only one case the 

 metatarsi at Enfield in which the variations are 

 about equal on each side of the mean. Perhaps 

 definite variation was here over-ruled by selection ; 

 but the results are so irregular that they must, I 

 think, be called indefinite. 



:< Definite variation " only means that a variation, 

 gradually increasing in intensity, is transmitted by 

 a number of individuals from one generation to the 

 next. While "indefinite variation" means that 



