CHAPTER XIX 



THE PARTICULATE THEORY OF HEREDITY AND 

 THE NATURE OF THE GENE 



The attempt to explain biological phenomena by means 

 of representative particles has often been made in the 

 past. The superficial resemblance of the theory of the 

 gene to some of the older theories, long since abandoned, 

 has furnished the opponents of the Mendelian theory of 

 heredity an opportunity to injure the latter by pretending 

 that the modern idea of the gene is the same as the older 

 ideas of Herbert Spencer concerning physiological units, 

 of Darwin relating to pangenes, and especially of Weis- 

 mann about biophors. There is no need for such con- 

 fusion, for even a little knowledge of the evidence on which 

 the old and the new views rest ought to have sufficed to 

 make evident some important and essential differences. 

 It need not be denied, however, that there is an historical 

 connection between the mediaeval theory of preformation 

 and the particulate theory of heredity. Bonnet, one of the 

 best known adherents of preformation, believed at first 

 in *' whole *' germs, but later admitted that pieces of germs 

 might be stowed away in regions of the body likely to be 

 injured. Weismann, also, the most prominent modern 

 adherent of preformation, held that whole germs, ids, are 

 present in the germ-plasm, each standing for a whole 

 organism — each (or most or one?) becoming unravelled as 

 the embryonic development proceeded. In fact, Weis- 

 mann 's entire theory was invented primarily to explain 

 embryonic development rather than genetics. Its connec- 

 tion with the modern idea of the germ-plasm is little more 

 than an analog)^ — for reduction in "Weismann *s original 

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