VARIATION. 16 VARICOSE VEIN. 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; anil the anteun;e 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 espeeiall}' 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 bj' 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). Correlated variation is the term applied to the common case of two organs so interdependent that when the one varies the other varies like- wise. Multiple parts, such as the segments of an earthworm, vary just as different individuals do and follow the same laws, and where one of these repeated parts varies, they all vary in the same direction. Thus, if a peculiar spot appears in one segment of a leech, it is apt to appear in the whole series of segments; also, a variety of a species characterized by one peculiarity is apt to be characterized by a whole series of peculiar- ities. The variability of the various elements of a series or multiple repeated organ differs in the difi"erent cases. For example, the spots on the thoracic shield of a potato beetle are sometimes constant in size and occurrence ; in others, the reverse. In the case of linear series, like the series of teeth on the jaw, it is often true that the terminal members of the series are the most variable. In general, the rule holds that si>ecifie characters are more variable than generic ones. But the relation between species and varying characters is even closer, as examination of ex- treme types will show. There is thus such a relation between the species of a genus that each, while maintaining its peculiar modes, varies espe- cially in the direction of the others. A species remains constant only in a constant environment. This is illustrated in every estuary, where the mollusks foimd up toward the fresher water are smaller than those in the open sea. Insects are darker along the seaeoast. So plants growing in cellars are long, and the leaves small and far apart, as compared with those living in the sun- light. Mountain plants arc smaller than those of the valley. A passage from one part of the country to another shows that animals gradually become dissimilar, and even the imlividuals of the same species undergo a change which may be apparently quite independent of environment. This is shown in the Galapagos Islands, who.sc climatic conditions are practically the .same, yet on each island the lizards are peculiar, and only one kind of lizard occurs on an island. BiisLiOGBAi'HY. Darwin, The Variation of Ani- mals and Plants Under Domestication (London, 2d ed., 1875); Galton, Natural Inheritance (ib., 1889) ; Bateson, Materials for the Study of ^'ariatiotl (ib., 1894) ; Pearson, The (Jrainmar of Science (ib., id ed., 1900). VARIATION. In music, a transformation of a melody by melodic, harmonic, contrapuntal, and rhythmic changes. The subject chosen is called the theme; it is first simply harmonized with or without an introduction, and then re- peated in a variety of forms. The oldest varia- tions are the doubles, in which the fundamental theme was not altered. But since the time of Haydn and Jlozart the form of the variation has become more artistic. The theme appears with new harmonies, the mode is changed from major to minor or vice versa; there is variety of key and rhythm, and the melodic intervals themselves are often altered. Frequently a new melody is added as a counter-subject to the orig- inal theme. The only principle to be observed is that the original theme shall always be recog- nizable by some feature. VARIATION OF LATITUDE. See Lati- tude, V.RIATIOX OF. VARIATION OF MAGNETIC ELE- MENTS. See ilAGNETiSM, Terkestrial; Com- PA.SS. VARICELLA. The medical term for chicken- pox (q.v. ). VAR'ICOCELE ( from Lat. varix. dilated vein, from varus, bent, stretched, knock-kneed, awry + Gk. K-qXri, kelc, tumor). In surgery, a vari- cose state of the veins of the spermatic cord. It is caused by the same conditions which give rise to varicose veins (q.v.) elsewhere. The symp- toms and treatment may be found in Dennis's System of Surgery (Philadelphia, 189.5-96). VARICOSE VEIN (Lat. varicosus, full of dilated veins, from varix, dilated vein), or Varix. A dilated and tortuous vein. Varices are of com- mon occurrence in the submucous veins of the rectum (constituting hemorrhoids or piles), in the spermatic veins, giving rise to varicocele (q.v.), and in the veins of the lower extremities. They are very rarely found in other veins, such as those of the scalp, neck, and groin. Cooks, wash- er-women, and soldiers and others whose occu- pation involves much standing, are specially prone to varicose veins. Varices may occur at almost any period of life, but are chiefly devel- oped during middle age. Their formation is aided by any condition of the system which im- pedes the circul.ation, as certain diseases of the heart, lungs, and liver, and by continued over- eating and the use of .alcoholic stimulants, which are liable to induce hemorrhoids. Senile degen- eralion, gout, pregnancy, and the excessive exer- cise of the athlete may act as causes in certain cases. In varico.se veins the coats of the dilated vessels may become thickened or may become thin; they may be lengthened so that the veins beeonur tortuous; (he dilatation may be unequal, giving rise to the formation of pouches; and, in conseqience of the enlarged calibre of the vessels, the veins act iin])erfi'ctly, and their walls gradually undergo degeneration. Varices oct'urring in the leg conunonly give rise to deep-seated aching pain in the limb, with a sense of weight, fullness, and numbness, before there is any external appearance of the affection. In a more advanced stage the ankles swell in the
