EFFECT OF TEMPERATURE ON CROSSING OVER 
191 
full line for the first eight or ten days. It later coincided with 
the control after all the eggs were laid which had passed the 
critical period — when crossing over probably occurs — at the 
high temperature. No section of the first chromosome tested, 
therefore, shows any effect of high temperature on the amount 
of crossing over. This is a complete confirmation of my earUer 
conclusion, made on less exact data, and for a much shorter 
13 
H. 
scute-echinus 
~ 1 
9 
1 
1 
7 
5 
1 
22 
20 
18' 
1 _ 
. 
1 
1 
1 
1 
echinus-cut 
16. 
' 
' 
— ' 
1 
14 
;. __-ji: — 
16 
1 
[ 
out-yerralllon 
14 
( f 
- 

1 
1 
12 
im 
17 
Termlllon-eamet 
1 
lb 
1 
lu- 
, 

ll 
1 -- 
9 
18 
garnet -forkert 
16 
14 
1 
1 
1 
' 
12 
10 
1 1 
_ ! ; 
--- 
i V 
10 
lb 
17 
?4 31 
Fig. 1 Curves of crossing over for different regions of chromosome I. The 
control values are the solid lines; the values from the heat-treated lines are 
dotted. The abscissas are days after mating, the ordinates percentages of 
crossing over. 
section of the chromosome. Second, a comparison of the differ- 
ent control lines with each other indicates no significant variation 
as the female grows older. The control line for second chromo- 
some regions dropped steadily up to about the tenth day, and 
gradually rose up to about the twenty-second. The sex chromo- 
some control values show no significant nor uniform changes, 
and confirm the conclusion of Bridges ('15) that in this chromo- 
some the age of the female has no influence on the amount of 
crossing over. 
