638 J\'Juclcs of tlic Hereditary Characters. 



support the main thesis, and attacli little importance to 

 the transportation hypothesis. 



Galton supposes that the various cells of the body 

 are originally represented l)y special material vehicles. 

 These vehicles combine to constitute the stirp which is 

 practically the same as the idioplasma.-^ Many more ve- 

 hicles must, however, be present in the germ than there 

 are actual types of cells. The remaining latent particles 

 ])lay a still more important part in Galton's theory than 

 they do in Darwin's, both in the explanation of onto- 

 genetic development and of atavism. The germ sub- 

 stance is handed down unchanged in the cell divisions 

 as well as in the multiplication of the individuals. It 

 is only under certain circumstances that changes appear 

 in it ; an assumption, which is obviouslv necessary for 

 the explanation of the transformation of species. 



In an extraordinarily clearly wn-itten hook on hered- 

 ity \\". K. Brooks has also suggested a modification of 

 the theor}^ of pangenesis.- He does not reject the whole 

 transportation hypothesis, but confines it to the trans- 

 portation of a few particles in special cases, especially 

 when the organism undergoes any change, whether from 

 external or internal causes. A change in the environment 

 of a cell induces it to throw off particles, and therefore 

 to transmit to the offspring of the plant a tendency to 

 deviate in the corresponding ]:)arts of the body in the 

 same way fp. 8v3). The male germ cells are particularly 

 adapted to the purpose of collecting these particles and 

 transmitting them to the female germ cells. If a change 

 has once become heritable through the medium of trans- 



^Fraxcis Galton, A Theory of Heredity, 1875. 



-\Y. K. Brooks. The La7v of Heredity, a Study of the Cause of 

 Variation and the Origin of Lizing Organisms, 1883. See especially 

 pp. 80- TOO, 319, 327, etc. 



