Ill VARIABILITY OF SPECIES IN A STATE OF NATURE 57 



sidered to give the size of the bird), from the shortest 

 to the longest, and the same number of vertical lines are 

 drawn, numbered from one to twenty. In this case (and 

 wherever j^racticable) the body-length is measured from the 

 lower line of the diagram, so that the actual length of the bird 

 is exhibited as well as the actual variations of length. These 

 can be well estimated by means of the horizontal line drawn 

 at the mean between the two extremes, and it will be seen 

 that one-fifth of the total number of specimens taken on either 

 side exhibits a very large amount of variation, which Avould of 

 course be very much greater if a hundred or more specimens 

 Avere compared. The lengths of the wing, tail, and other parts 

 are then laid down, and the diagram thus exhibits at a glance 

 the comparative variation of these parts in every specimen as 

 well as the actual amount of variation in the twenty specimens ; 

 and we are thus enabled to arrive at some important con- 

 clusions. 



We note, first, that the variations of none of the parts follow 

 the variations of the body, but are sometimes almost in an 

 opposite direction. Thus the longest wing corresponds to a 

 rather small body, the longest tail to a medium body, while 

 the longest leg and toes belong to only a moderately large body. 

 Again, even related parts do not constantly vary together but 

 present many instances of independent variation, as shown by 

 the want of parallelism in their respective variation-lines. In 

 No. 5 (see Fig. 4) the wing is very long, the tail moderately 

 so ; while in No. 6 the wing is much shorter while the tail is 

 considerably longer. The tarsus presents comparatively little 

 variation ; and although the three toes may be said to vary in 

 general together, there are many divergencies ; thus, in passing 

 from No. 9 to No. 10, the outer toe becomes longer, while the 

 hind toe becomes considerably shorter ; while in Nos. 3 and 4 

 the middle toe varies in an oj^posite way to the outer and the 

 hind toes. 



In the next diagram (Fig. 5) we have the variations in 

 forty males of the Ked-winged Blackbird (Agelseus phoeniceus), 

 and here we see the same general features. One-fifth of the 

 whole number of specimens offer a large amount of variation 

 either below or above the mean ; while the wings, tail, and head 

 vary quite independently of the body. The wing and tail too, 



