269 



VIII. — Tlie Frohleiii of Sijnapsis. 



By Lancelot Hogben, M.A., B.Sc, Lecturer in Zoology, 

 Imperial College of Science and Technology. 



{Read June 16, 1920.) 



The attention which has been directed of late years by Duesberg^ 

 Cajal, Weigl, Guillermond, Gatenby and others upon the behaviour 

 of the intracellular inclusions in the germ cycle of animals and 

 plants has again called in question the Weismannian doctrine 

 relating to the genetic significance of the nucleus. In attempting 

 to correlate the phenomena of cell anatomy with our knowledge of 

 the hereditary mechanism there are two propositions which may be 

 stated at the outset as a basis of agreement. First, that in all 

 cases of biparental reproduction of which we have any knowledge 

 both parents contribute equally to the constitution of the zygote ; 

 secondly, that the only data in genetics which permit any legiti- 

 mate inference as to the behaviour of the substantial basis of 

 inherited characters during the germ cycle are those derived from 

 the pursuit of Mendelian experiment. The first must be borne in 

 mind in approaching any theories which attempt to distinguish 

 between "specific" and "generic" characters in the process of 

 hereditary transmission. The demonstration of paternal characters 

 in Echinoid generic hybrids by MacBride and Debaisieux, as also 

 the observations of Baltzer, Doncaster and others on chromosome 

 elimination, leave no justification for assuming that there is any 

 difference between the paternal and maternal moieties contributed 

 to the zygote, or, as Jenkinson believed, between the role of cyto- 

 plasm and nucleus respectively, in relation to the specific and 

 generic characteristics of the organism. At the same time we must 

 dismiss every sort of speculation upon heredity based on a consider- 

 ation of cell structure unsupported by experimental fact. When, 

 therefore, authors like Mot-tier declare that they only claim the 

 transmission of non-Mendeliancliaractersby the chondriosomes, etc., 

 it is hardly possible to treat sucli hypotheses with serious consider- 

 ation. There may be a mode of inheritance which on analysis 

 yields no evidence of segregation or factorial integrity ; but 

 whether there is or not, at present nothing is known of such a 

 mechanism as could provide a foundation for correlating the 

 behaviour of the cell elements with it. It must therefore be con- 

 ceded that at present genetic cytology has to build upon the data 

 of Mendelism ; and it may be safely said that such considerations 



