591.81 115 



IV 



' Nuclear Reduction ' and the Function of 



Chromatin 



EVERY student of biology who remembers the quickening effect 

 of the "Principles of Biology" on his own youthful thought 



will have Riveted Mr Spencer's announcement that a second edition 

 of this great work is in progress, and welcomed the return of the 

 master to his old pursuits and studies. None the less is it a 

 duty to point out that one section of the instalment which we read 

 with so much interest in the May number of Natural Science (vol. 

 xii. p. 307) presents a view of the occurrence of ' nuclear reduc- 

 tion' as being an antecedent of fertilisation, which is inconsistent 

 with clearly ascertained facts, and a physiological explanation that 

 is inapplicable to some of the cases where it takes place. 



I 



The following remarks should have found their correct place in 

 a paper on " The fundamental Principles of Heredity,'" published in 

 Natural Sri, nee for October and November last, but were omitted not 

 to overweight it with details of a somewhat abstruse character, and as 

 lying apart from the main object of the study — the tracing out of 

 the cellular pedigree of the organism, with insistence on the point 

 that ' collateral cellular transmission ' was operative in all higher 

 organisms. And I would ask the reader to refer to my previous 

 paper in connection with the present one. 



' Nuclear reduction ' is an easy process to define. When a 

 nucleus is about to divide, its formed matter resolves itself into 

 a definite number of segments ; these split each into two, one 

 of which is destined to either of the daughter nuclei resulting 

 from the division. These segments have received the name of 

 ' chromatomeres ' or ' chromosomes ' ; we shall use the shorter, as 

 the more generally received one, though the longer does not carry 

 with it the numerous hypothetical implications, mostly wrong, of 

 the other. Usually, a nucleus on the approach of division reveals 

 the formation of as many segments as entered into it at its forma- 

 tion ; and thus the number of segments remains constant from 

 (cell-) generation to generation in the same species; but at a certain 

 point in the life-cycle the number of segments appearing on division 

 is smaller than at the previous divisions of the cells of the parent- 

 cycle : and this is called ' nuclear reduction.' 



