CHAPTER JX. 



VARIATION. 



85. EQUALLY conspicuous with the truth that every 

 organism 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 

 numerous traits of minor importance. No two plants are 

 indistinguishable; and no two animals are without differ- 

 ences. 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 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 



