226 Animal Life and Intelligence. 



crossed " solid-hoofed " and ordinary pigs. The offspring 

 did not possess all four hoofs in an intermediate condition ; 

 but two feet were furnished with properly divided and two 

 with united hoofs.* Professor Eimerf has noticed that, in 

 the crossing of striped and unstriped varieties of the 

 garden snail, Helix hortensis, the offspring are either striped 

 or unstriped, not in an intermediate or faintly striped 

 condition. 



These facts are of no little importance. They tend to 

 minimize, for some characters at least, the effects of inter- 

 crossing. The variations which present this trait may be 

 likened to stable organic compounds, which may be in- 

 herited or not inherited, but which cannot be watered down 

 by admixture and intercrossing. It is well known J that, 

 in 1791, a ram-lamb was born in Massachusetts, with 

 short, crooked legs and a long back, like a turn-spit dog. 

 From this one lamb the otter, or ancon, breed was raised. 

 When sheep of this breed were crossed with other breeds, 

 the lambs, with rare exceptions, perfectly resembled one 

 parent or the other. Of twin lambs, even, one has been 

 found to resemble one parent, and the second the other. 

 All that the breeder has to do is to eliminate those which 

 do not possess the required character. And very rarely 

 do the lambs of ancon parents fail to be true-bred. 



Now, it can scarcely fail that such sports occur in 

 nature. And if they are stable compounds, they will not 

 be readily swamped by intercrossing. It only requires some 

 further isolation to convert the sporting individuals into a 

 distinct and separate variety. Now, Darwin tells us that 



* Darwin, " Animals and Plants under Domestication," vol. ii. p. 70. 



t " Organic Evolution," Mr. Cunningham's translation, p. 76. 



J Darwin, " Animals and Plants uuder Domestication," vol. i. p. 104. 



Similarly, from a chance sport of a one-eared rabbit, Anderson formed a 

 breed which steadily produced one-eared rabbits (" Animals and Plants under 

 Domestication," vol. i. p. 456). This is an example of asymmetrical variation. 

 Variations are generally, but not always, symmetrical. Superficial colour- 

 variations are sometimes asymmetrical. Gasteropod molluscs are nearly 

 always asymmetrically developed. Among insects, Anisognathus affords an 

 example of the asymmetrical development of the mandible. Our right-handed- 

 ness is a mark of asymmetry. 



