Toyama, MendeFs laws of heredity as applied to the silk-worm crosses. 327 



parents while the striped forms, when paired inter se, split up into 

 the pale white and striped forms, as do the yellow X white. 



Thus, 



The first cross generation : 



The second cross 

 generation : 



10 parents 



6 produce 

 uniform striped. 



23 parents 



4 produce 

 a niixturc of 



striped (50 °/ ) + pale-white (50' 



13 parents 



striped (5 11 3) -f- pale-white (1617). 

 (23,95 "/„). 



constant. 



striped only. 



striped -j- pale-white. y Q 

 (224S). 720 (24,25 °/ ). 



10 parents 



The third cross generation: 



striped only. 



striped -\- pale-white. 

 (550) 199 (26,56 °/ ) 



This is an example of crossing cross-bred dominant forms with 

 the original recessive form. 



So it was ascertained that the larval rnarkings of the silk-worm 

 obey the Mendelian laws of heredity, as it is the case with the 

 colonrs of cocoons. 



III. 



Dihybrids. 



A. Crosses between no-marking yellow breed and striped white breed. 



In this reciprocal crosses, both parents possess two antagonistic 

 characters, larva without rnarkings and yellow cocoons in one breed, 

 striped larva and white cocoons in the other. 



The former breed is pure, while the latter sometirnes produces 

 no-marking white worms or a cross-bred form between "striped 

 whites" and "no-marking whites". 



The first «ross generation. 



In the first reciprocal crosses, the offspring produced by twenty 

 one parents were all striped yellow, while the rest (13 parents) 

 produced a mixed offspring consisting of striped yellow (1918) and 

 no-marking yellow worms (1869) and so approximately in the Pro- 

 portion of 1 : 1). 



