In 1850 the first house sparrows of Europe were introduced into this country, and from that time to 1870 upwards of 1500 birds are said to have been brought from the Old World (Merriam-Barrows, '89). To these introduced birds the environment has been novel. They have found abundant food, convenient and safe nesting places, practically no natural enemies, and unrivaled means of dispersal. Aside from an early and brief period of fostering care, they have been left to shift for themselves; natural agencies have since been at work, and in the relatively short space of forty years a continent has been, not merely invaded, but inundated by an animal which, in its native habitat, has been fairly subservient to the regulations imposed by competing life.

It seems to the speaker that here is an excellent example of the suspension of natural selection, for here, at least as far as certain external factors of selection are concerned, Nature does not select. Nearly all the young birds reach maturity; variations in color and structure, unless most extreme, are apparently not disadvantageous to their possessor; and if these variations are heritable, they do not seriously handicap the individuals of the next generation. A considerable departure in nesting and breeding habits does not jeopardize the domestic interests, and the simple mode of life permits even the weak individuals to endure. We conclude, then, that there is evidence to prove the first proposition, viz., in a specific case and in respect to certain characters, the operation of natural selection has been suspended.

For a proper discussion of propositions 2, 3, and 4, it was my first purpose to collect a large number of the American birds and compare them directly with an equal number collected. in England; but the labor and expense involved made this procedure inexpedient. The egg of the bird, however, is easy to secure, readily preserved, and can be purchased from European dealers for a relatively small price. It presents a remarkable range of variation, both in shape, size, and color, and offers certain fixed and readily measurable features which are not presented by the bird itself. Moreover, my observations lead

me to think that it is a structure which indicates departures from "normality" in a remarkable way. At all events, the variations, though they may present greater amplitude, are of the same inductive value, qualitatively, as variations of the skeleton, feathers, or other adult structures. The egg may

be taken, then, as a convenient and inexpensive means for the solution of at least some of the questions bearing on the subject of Panmixia.

At first, one hundred eggs, imported from an English dealer, were compared with an equal number collected in Providence, R. I. The dissimilarity in the two lots of eggs was so striking that I felt there must be some mistake, and at once imported. another hundred from a different locality, collecting in the meantime a second hundred of American specimens. On comparing the two enlarged collections, such interesting variations were found that I ordered all the English eggs that could be procured, and collected extensively from certain localities at home. At the close of the summer, 1896, I had 1736 eggs, one half of which were European, the other half American. These eggs, 868 foreign and 868 native, were compared (a) with respect to length, (b) ratio of length to breadth, (c) general shape, and (d) color. These comparisons ought to reveal any tendency towards increase of variation on the withdrawal of natural selection, that is, they ought to yield evidence in support of the second proposition. The data may be conveniently arranged in "curves of frequency."

If we erect on a base line (Diagram I), extending from 18 mm., which represents the shortest egg, to 26 mm., which represents the longest egg, a series of ordinates representing in sequence the added increment of 1⁄2 mm., and arrange on these ordinates the eggs that measure respectively 18 mm., 18.5 mm., 19 mm., 19.5 mm., etc., it is evident that the mean ordinates will be occupied by a considerably larger number of specimens than the extreme, and that the ascending and descending curve will indicate the general plan of the distribution of variation around the mean. Now if a species or structure is stable and shows only a slight tendency to vary, the base of the curve obviously will be short. If, on the con

DIAGRAM I. Curves of Absolute Lengths. -The distribution of the American eggs is represented by the broken line; that of the British eggs by the unbroken line.
The short eggs are at the left, the long eggs at the right. The number of specimens of each length is represented by the height of the respective ordinate;
thus there are 80 British and 119 American eggs which have a length of 20.5 mm.

trary, a species is unstable and has a general tendency to vary, the base will be long.

The 868 American eggs arrange themselves in respect to lengths as represented by the broken line on Diagram I. The base of this curve is long. Its summit coincides with the ordinate of 21 mm. Its interest, of course, lies chiefly in the relationship it bears to the curve of British eggs.

The latter curve is represented by an unbroken line. Its base extends from the ordinate of 18.5 mm. to the ordinate of 25 mm., and its point of greatest altitude is upon the ordinate of 22 mm.

A moment's examination of these curves reveals not only the fact that the American eggs are more variable, i.e., the base of the dotted curve is broader, but it also yields data appropriate to the third and fourth propositions; for it will be observed that the American eggs have undergone a striking reduction in their average length, that is, they show a departure from a previously maintained higher standard, viz., 22 mm. in length, and they are also tending to gather about a new point of equilibrium, viz., 21 mm. in length.

Without commenting upon these observations, which are based upon absolute measurements, let us see if the ratio of the breadth of the egg to the length, that is, the shape of the egg, has also been affected by the withdrawal of natural selection.

The curves on Diagram II are designed to represent the distribution of eggs according to the ratio of their major and minor diameters. When an egg approaches sphericity, the ratio is higher; when it is elongated, the ratio is lower. The more elongated eggs are arranged at the right of the diagram; the short, stumpy ones are arranged at the left. Oval and ellipsoidal eggs naturally occupy positions along the middle ordinates. The broken line, as before, represents the distribution of American eggs, the unbroken line, of British.

On this diagram it will be noted that the American eggs again show a greater amplitude of variation, the base of the dotted curve being nearly one-fifth broader than that of the entire curve. It will also be noted that, appropriate to the third proposition, the American eggs have undergone a striking

62% 61%
The more

84% 83% 82% 81% 80% 79% 78% 77% 76% 75% 74% 73% 72% 71% 70% 69% 68% 67% 66% 65% 64% 63% DIAGRAM II. Curves of Shape. - The distribution of the American eggs is represented by the broken line; that of the British eggs by the unbroken line. nearly spherical eggs are at the left, the more elongated at the right. For example: the figure 84% indicates that the shorter axis of the egg is to the longer as The number of specimens of each particular shape is represented by the height of the respective ordinate; thus, there are 95 British and 114 American eggs 84: 100. in which the breadth is 73% of the length.