188 Toyama. 
Back-crossing. 
(1) Hybrid black worms >< red. 
The results. Red worms .80 + black worms 481 (reciprocal crosses). 
Pure black worms >< red. 
The first generation All black worms (15 matings). 
— 
to 
The second generation 231 matings 
Red (8,173) + black (24,098). 
Summary. 
’ 
I. The sport “red worms’ may arısed from the normal black 
breed by crossing which apparently bring about the segregation of 
the dominant character. 
2. The red worm thus produced remains constant from its first 
appearance. It is recessive toward the ordinary black worms and 
segregates from the latter according to the Mendelian law of heredity. 
3. Sometimes it happens that the segregation of both characters 
is not complete, as in the case observed by Correns’) in plants. 
4. In the experiment described in a previous paper?) we obtained 
a new form quite different from the parents. We may mention 
another case, in which “blue worms” and brindled worms or ‘“Kasuri” 
arose spontaneously from the normal worms. All of them, however, 
were results of crossing and are quite constant from their first 
appearance. Any instance of pure mutation not yet observed. Hence 
we are now inclined to believe that the sporting which aise commonly 
met with in the silk-worm is mostly due to hybridization, that is to 
say, hybrid-mutation as Lidforss®) says, and not mutation in the 
sense of De Vries. 
1) Correns, Scheinbare Ausnahmen usw. Ber. d. d. Bot. Gesell. Bd. 20. 
2) Toyama, Studies on the hybridology of insects. 1. Bull. of Agric. coll. 
vol. 7. 1906. 
3) B. Lidforss, Studier öfver artbildningen etc. Archiv f. Botanik Bd. 4 1905. 
