326 
Francis B. Sumner 
The parent mice, after they had been exposed to these temperatare 
extremes for about six months, were paired for a second time on 
May 2, 1909. The resulting offspring are those to which attention 
will henceforth be devoted in this paper. 
The demands of our problem would have been realized more 
Fig. 4. 
7 8 9 10 11 12 13 14 15 16 17 IS 19 20 21 22 
Toot and ear length of same mice as those represented in Fig. 3. 'Sote that the vertical scale is five 
times as great as in the preceding figure. 
completely had the two contrasted sets of parent mice been transferred 
to a common room before pairing. Unfortunately this was not done^). 
Indeed the females were not removed to such a room until each was 
\ My failure to do so was the result of deliberate intention. At the time 
of pairing this lot, I had in hand another lot of modified individuals which I 
expected to pair later under temperature conditions which should be identical 
for the two sets of parents. I should thns be able to perform both of these 
experiments, and further restrict the possibilities of interpretation. Circum- 
stances prevented the fulfilment of this plan. 
