



AS CAUSE OF THE APPARENT CONSTANCY OF THE MUTANT „SPREAD”. 329 
1:1 is easily to be understood. I am sorry to say that it is impos- 
sible to make a closer examination as to whether such a supposed 
mistake might have taken place. 
When mating Old Spread to Old normal an equal number — as 
will be seen from table I — of New Spread and of New normal 
in F, were produced. That the New Spread type genotypically is 
otherwise than the original one, and in accordance with the theory, 
appeared from tables III and IV. — We are now going to examine 
whether the New normal type also behaves otherwise than the 
original one. As we know the New normal type in distinction from 
the old one contains the lethal factor vif. 
As to back-crossing of New normal with Old normal the offspring 
of course, will all be normal-winged, for the factor Spread is not 
found in any of the types. Only a single crossing of this kind has 
been counted (table V). 
V. New normal X Old normal. 






Th 1 spr Vit spr Vit _ | spr Vit — | | Sbr_vit vit 
SNE spr vit spr Vit spr Vit ‘ | spr Vit 
Sr eter £ normal | normal 
heee (old type) | (new type) 
Normal 
22 dd 



| 
K 29 | 67 68 
Also mutual crossing of New normal individuals must give nothing 
but normal winged individuals namely 2 New normal : 1 Old normal. 
17 such crossings have been made (table VI) and all the 2596 
offspring individuals appeared to be normal-winged. 
VI. New normal x New normal. 
Vit Vit 
Theoretically: tise x Ld 
spr vit spr vit 
SPORE |e spre vith). spr vit | | spr vit 
spr Vit |‘ spr vit “spr Vit | “spr vit 
normal normal normal | dies 
Phenotype: | 
(old type) | (new type) (new type) | 
