An Experimental Study of Somatic Modifications etc. 
335 
♦the curves (Figs. 6 and 7) for mice whose parents alone had been 
modified. 
We may likewise compare the figures expressing the mean 
differences, computed according to the principle just stated: 
Mice directly Oflfspring of modified 
modified 1) individuals 
Tail 9.710 1.264 
Foot 0.7138 0.1890 
Ear 0.2021 0.1281 
Comparing these two sets of figures, we find that the difference 
in tail length is 13 per cent as great in the second case as in the 
first; the difference in foot-length is 26 per cent as great, while the 
difference in ear length is 63 per cent as great! These figures are 
not offered as expressing, with even a rough degree of approxi- 
mation, the proportional part of these parental modifications which 
is handed on to the offspring — even granting that it is handed on 
in any strict sense of the words. The relative magnitude of the 
three percentages is particularly surprising, in view of the fact that 
the tail is the organ which responds most decidedly to the tem- 
perature differences, while the ear has been shown to be the least 
affected. It might be argued that the very plasticity of a part, which 
makes it so responsive to outside influences, might render it corre- 
spondingly ill-adapted to retaining such impressions permanently 2). 
Such speculations would be decidedly premature, however. 
As already stated another set of measurements was made with 
this same lot of mice when they reached the age of about 31/2 months. 
By that time the numbers had been considerably reduced by death ^j. 
1] Comment may be made in passing upon the fact that in this lot the 
diflference in tail-length is over 1.5 mm greater than in the case of the parents, 
despite the fact that the temperature differences had been much greater for the 
latter. I will not lay much emphasis on this circumstance, however, since it 
has been shown in my earlier paper 1909} that different lots of mice may 
respond to a very different extent to substantially the same differences of tem- 
perature. 
It may be pertinent to point out, likewise, that the tail is far more 
variable than either the foot or the ear. 
3) A certain proportion had succumbed under the influence of the ether, 
at the time of the 42 -day measurements. Commencing with about July 1, I 
was prevented by other duties from giving proper attention to the animals. 
They were kept in a limited number of cages, and over-crowding was doubt- 
less responsible for many deaths. 
