7 .-- Variation of Tarsus and Toes.] [Illustration: FIG.

8 .-- Variation of Birds in Leyden Museum.] In order to meet the objection that the large amount of variability here shown depends chiefly on the observations of one person and on the birds of a single country, I have examined Professor Schlegel's Catalogue of the Birds in the Leyden Museum, in which he usually gives the range of variation of the specimens in the museum (which are commonly less than a dozen and rarely over twenty) as regards some of their more important dimensions.

These fully support the statement of Mr.Allen, since they show an equal amount of variability when the numbers compared are sufficient, which, however, is not often the case.

The accompanying diagram exhibits the actual differences of size in five organs which occur in five species taken almost at random from this catalogue.

Here, again, we perceive that the variation is decidedly large, even among a very small number of specimens; while the facts all show that there is no ground whatever for the common assumption that natural species consist of individuals which are nearly all alike, or that the variations which occur are "infinitesimal" or even "small." _The proportionate Number of Individuals which present a considerable amount of Variation._ The notion that variation is a comparatively exceptional phenomenon, and that in any case considerable variations occur very rarely in proportion to the number of individuals which do not vary, is so deeply rooted that it is necessary to show by every possible method of illustration how completely opposed it is to the facts of nature.