26o RECENT CYTOLOGY 



recently revived in a prominent manner in the English 

 translation of Weismann's book, ' The Evolution 

 Theory.' In this book, published in 1904, the bearing 

 of the Mendelian evidence upon the subject of inheri- 

 tance is practically ignored ; although, in the face of the 

 definite experimental information now rendered avail- 

 able, the younger biologists, at least, are beginning 

 to realize that the circumstantial evidence, formerly 

 so much relied upon, will in future constitute a much 

 less prominent feature in these discussions. 



Weismann's theory of inheritance, and the Theory 

 of Ancestral Heredity in its original form, are based 

 upon a common assumption, which is now shown by 

 Mendel's discovery to have been unfounded. This is 

 the assumption that all ancestors of the same degree 

 e.g., grandparents make a substantially equal con- 

 tribution to the hereditary qualities of the offspring. 

 Mendel has shown that in the case of particular 

 hereditary characteristics this is not the case. 



But if we venture to criticise Weismann's conception 

 in the light of more recent knowledge, it must not be 

 forgotten that biology, and especially modern cytology, 

 owes a great debt to Weismann. To Weismann is due 

 the conception of the isolation of the germ-cells from 

 somatic influences, a view which is in complete accord- 

 ance with the Mendelian view of the inheritance of 

 definite characters. And it was Weismann who first 

 emphasized the belief that the chromosomes represent 

 those parts of the nucleus which are specially concerned 

 in the processes of heredity. These conceptions 

 which, indeed, constitute an essential part of his own 



