HISTORY OF ZOOLOGY. 3 r 



only as " sports," i.e. as varieties of the same species. The 

 differences between the " sports" of our domestic animals 

 are in many instances so considerable that formerly they 



FIG. IA. English Carrier-pigeon. (After Darwin.) 



FIG. IB. English Tumbler-pigeon. (After Darwin.) 



were regarded not only as sufficient for the distinction of 

 good species, but even of genera and families. In the fan- 

 tail pigeon the number of quill tail-feathers, formerly only 

 12-14, has increased to 30-42 (Fig. ic); among the 



