THE AMERICAN NATURALIST [Vol. LI 



bred from such hybrids inter se. The potential variabil- 

 ity of the collie was very small, a few years ago. Hybrids 

 with the Eussian wolfdog have been taken up into the 

 species. For this reason the variability has been very 

 extensive during a number of years. And at present this 

 variability is reduced again, by selection. In the mean- 

 time "the species has been changed as a whole, the fashion 

 having changed and having made much of the possi- 

 bilities afforded by the cross. The collie, which formerly 

 was an intelligent, affectionate dog, with a head shaped 

 like a fox; inclined to be noisy, and to run after every- 

 thing; with long straight, outstanding hair, and with color 

 ranging between black and tan, and sable, with a variable 

 •amount of white, has changed completely. The show 

 collie now is rather a treacherous and surly dog, with a 

 head shaped like that of a llama, silent and lazy, with hair 

 which inclines to be soft and wavy. The color is' much 

 more variable and now includes white, slaty, creamy, and 

 generally fade tints. 



In chickens, crossing is a common way of ''improving" 

 a species, and in all those instances we happen to know, 

 the hybrids were made by using an individual presenting 

 a character which it was thought desirable to fix into the 

 breed, or a certain degree of development of a character, 

 not reached by even the best individuals. Such an indi- 

 vidual used for crossing is sometimes a pure-bred animal 

 of another species, but much more often a mongrel of un- 

 known extraction, happening to be somewhat like the 

 breed to be improved, with the exception noted above. 

 It is the practice to breed the hybrids obtained from the 

 cross back to the species, and their offspring again, 

 always selecting those individuals which come nearest to 

 the general conformation of the species, but which have 

 the character to be fixed into the breed. For instance 

 one may want to breed blue Wyandottes. The breeder 

 will then take any blue fowl which happens to look some- 

 what like a Wyandotte, mate it into a strain of first-class 

 ^^^hite or black Wyandottes, breed the hybrids back into 



