f!l4 Toyaraa, On certain characteristics of the Silk-worm etc. 



Before entering upon the subject, we shall enumerate the normal 

 Mendelian characteristics found in the silk-worm during the last 

 five years. In my first experiments on the breeding of silk-worms 

 published in 1906, we came to the conclusion that "of various 

 characteristics of the silk-worm, some strictly follow Mendel's 

 laws (colours of cocoons, larval markings etc.), while others obey 

 certain other law r s which are not to be clearly formulated as Men- 

 del's (such as voltine characters)", concerning the latter of which 

 McCracken 1 ) arrived at the same conclusion in her paper published 

 in 1909. An investigation made by Kellogg 2 ) (1908) gave a similar 

 result. He says "Larval colour-pattern differences are consistently 

 and rigorously alternative and Mendelian in inheritance" and "cocoon 

 colours tend to be alternative and Mendelian in behaviour but are 

 inconsistent as to dominancy and recessiveness and numerical propor-* 

 tions, and may even break down and blend, or one colour be 

 otherwise influenced or modified by the presence, in a mating, of 

 another. Thus sweeping generalizations concerning the inheritance 

 behaviour of the cocoon colours tending to class them unqualifiedly 

 in the Mendelian category can not be made. The tendency is for 

 them to behave in Mendelian manner, but it is a tendency subject 

 to numerous, marked and various inconsistencies and irregularities." 



Now we shall briefly enumerate the various characteristics of 

 silk-worms studied by us since 1907. 



Larval Characteristics. 



1. "Exuviation." Certain breeds of the silk-worm moult four 

 times during their larval stage, while others only moult three times. 

 We call the former tetra-moulting worms and the latter tri-moul- 

 ting. Most of the good breeds now in vogue belong to the former 

 class. These are Mendelian characteristics, the tetra-moulting being- 

 recessive to the tri-moulting There are found sometimes to- 

 rn oulting worms among ordinary tetra-moulting ones. In this case, 

 the characteristic is not transmissible to the offspring. We believe 

 now that it is caused by certain external influences. 



2. The colour of the blood. In the silk- worm, there are 

 two sorts of breeds, the one being yellow-blooded and the blood 

 of the. other being colourless. All the former spun yellow or 

 some other coloured cocoons, while the latter are mostly white 

 cocooners, rarely green or canary yellow cocooners. These character- 

 istics come also in the Mendelian category, the yellow blooded being 

 dominant towards the colourless. Most European yellows belong 

 to this category. All the green breed are colourless. 



1) McCracken, J. - - Heredity of the race-characters univoltism and bivol- 

 tinism in the silk-worm. 1909. 



2) Kelogg, L. - Inheritance in silk-worms. 1908. 



