CHAPTER V 



THE 'ids' and 'determinants' OF WEISMANN VERSUS THE 

 'physiological units' of HERBERT SPENCER 



THE general acceptance of the Doctrine of Evolution initiated 

 by the publication of Darwin's epoch-making work, "The 

 Origin of Species," soon attracted enormous attention to the 

 problems connected with Heredity ; and some of these doctrines in 

 their turn have sufficed to focus the labours of a vast number of 

 workers upon the structure of cells, and upon the excessively com- 

 plicated processes commonly taking place in such bodies when 

 they divide, and more especially upon the processes occurring in 

 those particular cells — the germ cells and sperm cells — upon whose 

 union the development of different animals and plants for the most 

 part depends. 



The result has been a vast amount of scientific hterature 

 dealing, both theoretically and experimentally, with the subject of 

 Heredity,' and one equally vast on the subject of Cytology — that 

 is concerning the structure, functions, and life history of cells. To 

 some of these discussions a brief reference must now be made. 



What has already been said in previous chapters should have 

 made it perfectly clear, that we must look for the fundamental 

 properties of living matter as being possessed by certain chemical 

 units of great complexity, though so minute as to lie altogether 

 beyond the range of any existing microscopical powers ; and, 

 further, that such invisible units when they grow, by the con- 

 tinuance of synthetic chemical processes, result in the appearance 

 of minute particles of protoplasm which, though structureless, 

 speedily assume one or other of the well-known forms of lowest 

 organisms. We have, moreover, seen reason to believe that such 



" The modern discussions on this subject may be said to have been initiated 

 by Darwin's hypothesis of "Pangenesis," published in 'Animals and Plants 

 under Domestication," 1868, Vol. II., p. 357. An improved form of this 

 rather crude hypothesis has since been put forw^ard by Hugo de Vries, in his 

 " Intrazellulare Pangenesis," Jena, 1889. 



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