NOMENCLATURE. A variant is one of the dis similar conditions of form in which an organ ap pears; thus the vat hints of the number of rays of n scallop-shell are 13, 14, 15, etc. .\ variant, must be sharply distinguished from a variety, which is a group term for individuals that breed true to one another, and resemble one another in color, size, and other characteristics less broad and general than specific ones. A variate is one of the varying units of study: each scallop-shell is, in respect to the number of its rays, a variate, :Ind in 1000 scallops there may be. for example, 200 variates (ray-numbers) falling in the variant class of 16 rays. Each different variant thus usually includes a number of variates. Variates are of 'No sorts: counted and measured (inte gral' and 'graduated' For example, the number of rays on a scallop-shell (15, 16. 17, etc.) is an integral variate; the diameter of the shell is a gradual oil variate. The data of variation may be classified in various ways, but two main types are (1) slight variations and (2) sport variations. Slight variations are such apparently trivial dif ferences as distinguish one adult male of a homogeneous community from another male of this community, one grain of wheat from another •rain of wheat, the number of grains on one head of rice from the number on a second head of rice. It is the noticed and yet unnoted form of variation. Sport variations arc the relatively rare occurrence of great differences cropping out in a community. These are sometimes incom patible with life, and are then known as 'mon sters;' but when sports persist, and are bred from, they may impress themselves with peculiar strength; e.g. Ancon sheep, and the hair less peaches called nectarines. Variable char acters may also be classified as 'integral' and `graduated.' They play a nearly equal part in evolution, for some species have differentiated chiefly along the line of multiplication or reduc tion of the number of parts, while other species have varied in size, color, and other qualities of parts. Again variates may he either individual or organah Individual variates belong to dif ferent individual animals or plants, whereas or ganal variates are found in the multiple organs of one and the same individual, e.g. the length
of a fish is an individual variate; the diameter of one of its scales as compared with that of the others is an organal variate. According to Huxley's definition, "a race is a propagated variety." These terms, variant, variety, race, species, are by no means fixed, since in many in stances gradations may be found which more or less completely link them.
Variation with age is a matter of daily observa tion. First of all the absolute size of the body and its organs tends to increase with age up to a limit. Secondly, the proportions change. Some organs are developed precociously, for instance, the child's head: others are retarded, e.g. the length of the child's legs. Careful measurements of the shell of a crab have shown that the shell grows larger in proportion to its breadth as it grows older. Especially at the time of sexual maturity in most animals special features de velop greatly that are earlier latent. Not only the size. but also the variability of organs. changes with age. Thus the standard deviation of the stature of the 5-year-old child is 3 inches; of the 7-year-old child 2.S5 inches. Variation with sex is likewise a widespread phenomenon. Not all organs vary in the two sexes, however, but only the so-called secondary sexual ones, such as the mane of mammals: the comb, wattles, and tail feathers of fowl; the plumage of most birds; and the antenme of moths. The old idea that the male was uniformly more variable is not mark edly true. In the wings of some insects the female is the more variable.
The fact of selection is best measured by vari ability, any species after selection being pre sumably less variable than before: the mean also may be changed by selection if this acts especially on the large or on the small. By se lection we may, moreover, divide a binomial species into two pure groups each centring about one of the modes. Darwin and others have thought that by selection of minute variations a species might be changed to any extent, but this view is combated by some, especially De Vries, who maintains that selection of slight variations can improve qualities already present, but can not originate new ones, for which we must wait upon haphazard appearances (sports).