An Experimental Study of Somatic Modifications and 
their Reappearance in the Offspring. 
By 
Francis B. Sumner 
(Woods Hole, Mass., U.S.A.). 
With 11 figures in text and tables XVI— XVIIL 
Eingegangen am 3. Miirz 1910. 
For several years past the present writer has studied the effects 
of differing temperature conditions upon the growth of the white 
mouse. In a recent paper ^) some of these effects have been discussed 
rather fully. It has there been shown that the length of certain peri- 
pheral parts of the body (tail, foot and ear) is greater in individuals 
which have been reared in a warm room than in ones reared in a 
cold room. As regards the tail, the modification was found to be 
very striking, the mean length of this organ for the two sets of in- 
dividuals differing in one experiment by more than 30 per cent. In 
the case of the foot, the difference was less pronounced, but its real- 
ity was evident in every experiment. The ear, on the other hand, 
appeared to respond but feebly to temperature conditions 2). From 
determinations of the quantity of hair in two of these contrasted lots 
of mice, it was shown to be probable that this likewise was affected 
by sufficiently great differences of temperature. The extreme labo- 
riousness of these latter determinations has, however, rendered it im- 
possible thus far to deal with a sufficiently great number of indivi- 
duals to satisfy the demands of statistical theory. 
^) Journal of Experimental Zoology. August 1909. 
2; In my earlier paper, indeed, I expressed doubt as to the significance 
of such small differences as I did detect in the case of this organ. Further 
observations have, however, lessened these doubts. 
