vii HEREDITY, VARIATION 111 



correspondence with that of the body. No. 5, with a quite 

 short body, has the longest wing of all ; while No. 1 6, with a 

 long body, has nearly the shortest wing. The third line, 

 showing the tail-lengths, is equally remarkable, for No. 6 

 shows the longest tail with quite a short body, while No. 16, 

 with one of the shortest tails, has a long body ; so that Nos. 

 6 and 16, measured in the usual way to the end of the 

 tail, would be found of exactly the same size, though the 

 one is really f- inch shorter than the other. 



The next three lines show the varying lengths of the 

 tarsus (commonly termed the leg), the middle toe, and the 

 outer toe, and they too show very distinct and often 

 contrasted divergences in proportion to their small total 

 length. Thus Nos. 1 4 and 1 8 have nearly the shortest legs 

 with large bodies. The middle toe in 7 is as long as in 19 

 and 20, while the outer toe is decidedly longer than in 19, 

 and in 12 decidedly shorter than in 2. 



It is particularly important to note here that this remark- 

 able amount of variation occurs in only twenty birds taken 

 at random. But the species is one of the most populous in 

 North America, occurring in enormous flocks over the whole 

 continent, from 54° N. lat. in summer, and migrating as far 

 south as Paraguay in winter. There must, therefore, be an 

 average population of (probably) hundreds of millions, giving 

 a much greater range of variation, and an ever-present 

 abundance of variations of all the parts and organs of the 

 species. 



In my Darwinism (chapter iii.) I have given sixteen 

 diagrams of variation, showing that it occurs to an approxi- 

 mately equal extent in mammals and reptiles as well as in birds, 

 and in a large number of their parts and external organs ; while 

 many examples of variation occur among the lower animals, 

 especially insects, and also to an amazing extent among 

 plants. During the last twenty years an enormous amount 

 of work has been done in the investigation of variation in all 

 its phases and complexities, and an excellent account of 

 these has been given by Dr. H. M. Vernon in his Variation 

 in Animals and Plants, 1903 (International Scientific Series), 

 to which my readers are referred for fuller information, but 

 a few of his conclusions may be here given. He says : 



