Ill VARIABILITY OF SPECIES IN A STATE OF NATURE 59 



though showing some amount of correlated variation, yet in 

 no less than nine cases vary in opposite directions as compared 

 Avith the preceding species. 



The next diagram (Fig. 6), showing the variations of thirty- 

 one males of the Cardinal bird (Cardinalis virginianus), exhibits 

 these features much more strongly. The amount of variation 

 in proportion to the size of the bird is very much greater ; 

 while the variations of the wing and tail not only have no 

 correspondence with that of the body but very little with each 

 other. In no less than twelve or thirteen instances they vary 

 in opposite directions, while even where they correspond in 

 direction the amount of the variation is often very dispropor- 

 tionate. 



As the proportions of the tarsi and toes of birds have great 

 influence on their mode of life and habits and are often used 

 as specific or even generic characters, I have prepared a 

 diagram (Fig. 7) to show the variation in these parts only, among 

 twenty specimens of each of four species of birds, four or five of 

 the most variable alone being given. The extreme divergence 

 of each of the lines in a vertical direction shoAvs the actual 

 amount of variation ; and if we consider the small length of 

 the toes of these small birds, averaging about three-quarters of 

 an inch, we shall see that the variation is really very large ; 

 while the diverging curves and angles show that each part 

 varies, to a great extent, independently. It is evident that 

 if we compared some thousands of individuals instead of 

 only twenty, we should have an amount of independent 

 variation occurring each year which would enable almost any 

 modification of these important organs to be rapidly eftected. 



In order to meet the objection that the large amount of 

 variability here shown depends chiefly on the observations 

 of one person and on the birds of a single country, I have 

 examined Professor Schlegel's Catalogue of the Birds in the 

 Leyden Museum, in which he usually gives the range of 

 variation of the specimens in the museum (which are 

 commonly less than a dozen and rarely over twenty) as 

 regards some of their more important dimensions. These 

 fully support the statement of Mr. Allen, since they show an 

 equal amount of variability when the numbers compared are 



