4 BIOLOGICAL LECTURES. 



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 com- 

 paring 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 Ameri- 

 can. 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 with- 

 drawal of natural selection, that is, they ought to yield evi- 

 dence in support of th j second proposition. The data may be 

 conveniently arranged in "curves of frequency." 



If we erect on a base line (Diagram I), extending from 

 1 8 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 ^ 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 distribu- 

 tion of variation around the mean. Now if a species or struc- 

 ture is stable and shows only a slight tendency to vary, the 

 base of the curve obviously will be short. If, on the con- 



