LIBRARY 



NEW YORK 



BOTANICAL 



QARDtN 



Species crosses in Rats. 



By A. L. and A. C. Hagedoorn. 



(Eingegangen 25. Dezember 1921.) 



Introduction. 



With few exceptions, the breeding- experiments with animals have 

 consisted of analyzing- genetic differences which were given in one 

 species, generally a domestic species. Numerous genes have so become 

 known in the domestic mouse, in the laboratory rat, the rabbit, the 

 guinea pig. In these species crossbreeding is so common, that almost 

 all the possible combinations of genes affecting coatcolour have been 

 seen, and can be recognized in their result. This means, that generally 

 we can say with the first authors on the subject that in these groups 

 crossing and subse(|uent segregation recombine characters. Novel 

 characters, due to novel combinations of genes, can only be expected 

 in this material, when some new animals are imported from other regions. 

 This happened in I) arbi shire's work when he used Japanese mice for 

 crossbreeding experiments, and again in the work of Castle when he 

 imported South-American domestic cavies. 



As soon as we start crossing different natural species, however, 

 matters become more complicated. It has long been recognized by the 

 horticulturists, that speciescrosses produce noveties, new characters. 

 When a new daffodil or a new Canna is introduced, it is to say, if it 

 has never been used for crossing before. It is a common mistake to 

 believe, that the horticulturists value the new species according to its 

 possession of novel characters, which can be recombined with those of 

 the domestic species. Quite apart from its appearance, the new species 

 is valuable, because it is expected, that crossing with this species will 

 produce novelties, novel, hitherto unknown characters. No one but a 

 strawberry specialist would see any merit in a insignificant little plant 



Induktive Abstämmlings- und Vererbungslehre. XXIX. 7 



