CHAPTER IX. 



VARIATION. 



85. EQUALLY conspicuous with the truth that every organ- 

 ism bears a general likeness to its parents, is the truth that 

 no organism is exactly like either parent. Though similar 

 to both in generic and specific traits, and usually, too, in those 

 traits which distinguish the variety, it diverges in numer- 

 ous traits of minor importance. JSTo two plants are indistin- 

 guishable ; and no two animals are without differences. 

 Variation is co-extensive with Heredity. 



The degrees of variation have a wide range. There are 

 deviations so small as to be not easily detected ; and there 

 are deviations great enough to be called monstrosities. In 

 plants, we may pass from cases of slight alteration in the 

 shape or texture of a leaf, to cases where, instead of a flower 

 with its calyx above the seed-vessel, there is produced a flower 

 with its calyx below the seed-vessel ; and while in one 

 animal, there arises a scarcely noticeable unlikeness in the 

 length or colour of the hair, in another, an organ is absent, 

 or a supernumerary organ appears. Though small variations 

 are by far the most general, yet variations of considerable 

 magnitude are not uncommon ; and even those variations 

 constituted by additions or suppressions of parts, are not so 

 rare as to be excluded from the list of causes by which 

 organic forms are changed. Cattle without horns are fre- 

 quent. Of sheep there are horned breeds and breeds that 



