322 Toyama, Mendel's laws nf heredity as applied to the silk-worm crosses. 



1. Siaraese multivoltine whites X Siamese multivoltine 

 yellows, 



2. Siamese multivoltine yellows X Japanese univoltine whites, 



3. Japanese univoltine whites X European univoltine yellows. 

 Every breed above cited was reared by myself during five or 



more generations preliminary to the breeding experiments in order 

 to tost whether it is really a pure breed which spins cocoons of 

 a single fixed colour or not. 



Since the disintegration of parent characters occurred in 

 some of the second or third crosses the hereditary phenomena were 

 much more complicated here than those in the first cross (Siamese 

 whites X Siamese yellows) where no such phenomenon has been 

 observed. 



We will at first consider the simpler cases and then pass over 

 to the more complicated ones. 



A. Simpler cases. 



The first cross generation. 



When the "yellows" and the •'whites" are allowed to breed 

 together the first cross always gives yellow cocoons with no ex- 

 ception, in other words, the yellow character is dominant while the 

 white is recessive. 



The second cross generation. 



The offspring raised from this yellow form of the first gene- 

 ration produces two kinds of cocoons, yellow and white in the pro- 

 portion of three yellow to one white, namely in average: 



Number of parents White cocoons ' Yellow cocoons 



35 2,026 (25,03°/,,) 6,0(59 (74,96°/ ) 



In individual cases, the rates betvveen white and yellow cocoons 

 nuctuate between 21,64°/ : 78,35 °/ and 30,6%: 69,-i9°/ . 



The third and the following generations. 



In the third and subsequent generations, the white form pro- 

 duces oft'spring, all coming true to parents without exception, 

 while the yellow one, on the contrary, produces two kinds of 

 offspring, one spinning only yellow cocoons (which is called A form 

 hereafter), the other (called B form hereafter) yellow as well as white 

 in the proportion of yellow 75,1 °/ to white 24,8 °/ . 



Of the form A, we may distinguish two kinds, namely, 1. those 

 which remain constant throughout succeeding generations (form a), 

 2. those which when paired inter se, will again split into white 

 (about 25°/ ) and yellow (about 75°/ ) forrns (form ß). 



