[95]

(40

(Var. under domest)

Variation of Multiple Parts Laws of Variation Nature

(Whenever any part or organ is repeated many times over in the structure of a species, it is variable in number, without relation to its importance, this part of the body of same part of organ becoming numerically constant, in number, either in other parts of the body in the same individual, or in other species, whenever the number is few: what can be more inconstant than the number of the feathers on a birds body, yet in the wing & tail, these principal feathers are remarkably constant in whole genera & even Families; but in some of those genera which have an unusual number of caudal feathers, the number is found to vary in the same species. It might be thought that the greater importance of the wing & tail feathers would account for their constancy; but I doubt this; for we find the same rule in the vertebræ, which are generally constant in the each mammifers & Birds mammals & birds, but in snakes, according Schlegel, the number varies greatly in the same species. So I believe it is in the teeth of fish & reptiles compared with the teeth of mammals. In plants, in those species (a) which have many petals, stamens or pistils, that their number ‒ far more variable than when there are only few; & Gærtner good→ Kentniss Der Befruchtung s. 220, 364.— has remarked that the number of seeds is far more constant in those plants, which have few, than in the polysemous kinds. Why this rule is so general, no of the variability in number of any part or organ whether important in number which is already numerous, should

[95v]

Isidore Geoffroy's Law — Hist anomalies

Tome 3. p. 4 5 6.—

[Variation 2: 342: "On the Variability of Multiple and Homologous Parts.—Isidore Geoffroy6 insists that, when any part or organ is repeated many times in the same animal, it is particularly liable to vary both in number and structure. With respect to number, the proposition may, I think, be considered as fully established; but the evidence is chiefly derived from organic beings living under their natural conditions, with which we are not here concerned. When the vertebræ, or teeth, or rays in the fins of fishes, or feathers in the tails of birds, or petals, stamens, pistils, and seeds in plants, are very numerous, the number is generally variable. The explanation of this simple fact is by no means obvious. With respect to the variability in structure of multiple parts, the evidence is not so decisive; but the fact, as far as it may be trusted, probably depends on multiple parts being of less physiological importance than single parts; consequently their perfect standard of structure has been less rigorously enforced by natural selection.
6 'Hist. des Anomalies,' tom. iii. pp. 4, 5, 6."]

(a) text

According to Mr Wollaston it has been asserted that in insects having multi-articulate antennæ, the number of joints in the antennæ vary: in certain cirripedes the number of joints in the second & third pair of limbs, the number is usually pretty constant, but in Tetraclita their limbs are are one greatly elongated, & have very many articulations, & I could in these I could hardly find find two individuals with the same number.