62 INHERITANCE IN SILKWORMS, I 



by the worms of certain races, as the races of Japan and several of 

 China, to combine two or more in the same cocoon, that is to make 

 what are called double cocoons ; it seems, however, that in this respect 

 the hybrids tend more often to follow the female than the male. 



"Finally if one mates hybrids among themselves one will find in 

 the worms and cocoons a diversity of size, form and color much greater 

 than would be found in the direct descendants of the parents and this 

 great diversity in the cocoons depreciates them much in the eyes of the 

 spinners. 



"The principal advantages of these crossings is the production of 

 worms very vigorous and very robust which resist the disease of flaccid- 

 ity better than do the native races of yellow or white cocoons and 

 which give at the same time a tolerable harvest in places in which the 

 European races produce rarely a harvest worth gathering; besides 

 they are very much more precocious and form their cocoons sooner. 



"But aside from these advantages these crossings are disadvan- 

 tageous by producing worms and cocoons very often dissimilar, some- 

 times following more one race, sometimes more the other, and if one 

 intermates the hybrids one obtains products of a still greater diversity. 

 It is wise therefore to confine oneself to rearing worms issuing 

 directly from an original crossing and of repeating this crossing each 

 year. But for this it is necessary of course to make rearings each year 

 of the two pure races of which one proposes to make the crossings. 

 This is, of course, a disadvantage and a complication." 



These are practically all of the generalizations touching the "effects 

 of crossing" which the authors of this modern authoritative treatise on 

 silkworm culture permit themselves to express. Without doubt they 

 might, from the large experience and the long series of rearings carried 

 on by their station, utter many more. But, and this is the point to which 

 I wish to call attention, of how curiously indefinite and unsatisfactory 

 character are such generalizations compared with those which can be 

 expressed after even so few years of experimental breeding as those 

 of Toyama and myself in the light of the modern scientific study of 

 heredity. 



The knowledge of the definite Mendelian character of the inheritance 

 of certain characteristics and the knowledge that certain other char- 

 acteristics are not inherited according to Mendelian principles but must 

 be fostered and maintained by strict personal selection, can be a potent 

 help to the commercial silk grower in his attempts to produce new races 

 especially fit for his particular need and use. 



