134 BLASTOGENIC VARIATIONS. 



question is fraught with doubt and difficulty, and 

 greatly lacks the experimental data necessary for put- 

 ting it to an adequate practical test. Hence, for the 

 present, it is best to regard the matter as still sub 

 judice. 



The law of heredity and regression which we may 

 consider to have been substantiated for sweet peas, for 

 Basset hounds, and for man, may justifiably be ex- 

 tended to other organisms as well. It seems probable 

 that it is, in fact, to use Mr. Galton's words, " univer- 

 sally applicable to bisexual descent." As already 

 stated, however, it should always be borne in mind that 

 it deals only with average amounts, and not absolute 

 amounts. Though the law is of great value in the 

 breeding of pedigree stock, it is not exact enough to 

 enable one to predict with any accuracy the characters 

 of the unborn offspring of known parents, or even of 

 known grandparents as well as parents. Nevertheless 

 the mere fact of such a law of average inheritance 

 being demonstrable, indicates triumphantly how fun- 

 damentally important is the constitution of the germ- 

 plasm in the determination of variations. 



We see, then, that Weismann's conclusions as to the 

 chief factors concerned in the origin of blastogenic 

 variations are in the main confirmed, so far as it is pos- 

 sible to put them to an experimental test. It is 

 of course impossible to obtain experimental proof of 

 the actual existence of biophors, determinants, and ids 

 in the germ-plasm, but it is scarcely possible to account 

 for the facts of heredity without making some such 

 hypothesis. The Law of Ancestral Heredity proves 

 that all ancestors, however remote, are able to leave 



