10 INHERITANCE IN SILKWORMS^ 1 



Some of these latter characters cannot be controlled even by most 

 careful and persistent selection, and in this give a strong negative (as 

 do some of the characters of Leptinotarsa experimented with by- 

 Tower) to the familiar declaration of the selectionist that there is no 

 limit to the quantitative modification of characteristics by means of 

 selection. "Tell me what you want made out of this plant or animal 

 and I'll make it," exclaims the selectionist breeder. But most times he 

 can't, and in those times that he can he will most often do it by 

 hybridization, not pure selection. And this hybridization he will find 

 necessary despite the start in any direction he ought to get from 

 "infinite fortuitous variation." 



Contagne and Toyama. — Before setting out any of the data and 

 conclusions derived from my own work with silkworms I must call 

 attention to two previous studies, those respectively of Coutagne 

 (Recherches Experimentales sur I'Heredite chez les Vers a Sole, pub- 

 lished as No. 422, Serie A, Theses presentees a la Faculte des Sciences 

 de Paris, pp. 1-194, plates I-XI, 1902), and Toyama (Studies on the 

 Hybridology of Insects : I, On some silkworm crosses, with special 

 reference to Mendel's law of heredity, published in Bulletin of the 

 College of Agriculture, Tokyo Imperial University, vol. VII, pp. 259- 

 393, plates VI-XI, 1906). The work of Coutagne was done and his 

 thesis written without knowledge on his part of the experiments and 

 conclusions of Mendel and of Mendel's discoverers, De Vries, Correns 

 and Tschermak, but a part of the work done by the French student and 

 some of his results are distinctly in line with the Mendelian or alterna- 

 tive inheritance principles of heredity. Coutagne, however, gave his 

 principal attention and eflfort to the modification of fluctuating 

 characters, especially those of quantity and quality of silk, by persistent 

 selection. His work has been recognized and estimated pretty fairly 

 by such thorough-going Mendelian students as Bateson, and needs no 

 particular exploitation or summing up by me. 



Toyama's work, in contrast with Coutagne's, has been conducted 

 in the light of a full knowledge of Mendel's work and of that of his 

 successors, and has indeed been directly carried on to test the applica- 

 tion of Mendelian principles to silkworm inheritance. It is of interest — 

 of very lively interest, indeed, to me — to note how closely parallel 

 Toyama's work and that part of mine devoted to the same end have 

 been going on, each of us presumably without knowledge of the other's 

 work. We began at practically the same time — Toyama in 1900, I in 

 1901 — and have used the same characteristics in the same way with 



