Manchester Memoirs, Vol. l. (1906), No. 0. 23 



their changes some explanation might be found for the 

 problems of heredity and sex. 



It may be of some interest to examine the evidence 

 we have for considering the chromosomes the sole bearers 

 of hereditary characters. 



In 1866, Haeckel ^43, p. 288) wrote ' wir werden den 

 Kern der Zellen als das hauptsachliche Organ der Verer- 

 bung, das Plasma als das hauptsachliche Organ der An- 

 passung betrachten konnen." When the chromosomes 

 were observed we find Hertwig (47), Strasburger (87, 88), 

 and Weismann (104) considering them as the bearers of 

 the ' Vererbungsubstanz.' It was, however, considered by 

 many to be a proven fact that the chromosomes were the 

 bearers of the hereditary characters when Boveri (14) 

 made known his experiments on fertilising fragments of 

 Echinoderm ova.* He shook up echinoderm eggs in a 

 tube half filled with sea-water for some time. After this 

 rough treatment, he poured spermatozoa of another species 

 into the liquid containing whole eggs and fragments. In 

 this manner he obtained Plutei, concerning which he made 

 statements to the effect that there were a number of 

 small specimens, which he concluded came from frag- 

 ments of eggs ; as the nuclei of these same plutei were 

 very small, he concluded they came from enucleated 

 fragments ; also they bore pure paternal characters. 

 Therefore he concluded that the cytoplasm of the ovum 

 does not transmit any maternal characters ; it followed 

 then, that the nucleus alone was the bearer of the heredi- 

 tary characters. From this experiment it certainly 

 appeared as if the nucleus were the only part of the cell 

 concerned in the transmission of the hereditary characters. 



When these experiments were repeated by Vervvorn 



* O. and R. Hertwig (48) first attempted fertilising fragments of Echino- 

 derm ova. But their experiments were not conclusive. 



