HEREDITY AND EVOLUTION 95 



mals. In both cases he assumed that in addition 

 to the powers of division cells multiply by means 

 of minute germs or " gemmules," which are 

 thrown off by the somatic cells, collected from all 

 parts of the body to form the sexual elements, and 

 are " ultimately developed into units " (cells) 

 hke those from which they were originally de- 

 rived/ Pangenesis thus comprised two princi- 

 pal postulates, both of which had been in a meas- 

 ure foreshadowed by the speculations of Bonnet, 

 Buifon, and even earlier writers. One is the 

 particulate or meristic assumption that particular 

 hereditary traits are represented in the germ-cell 

 by discrete and specifically organized particles, 

 the " gemmules " or " pangens," that are capable 

 of self -perpetuation by grovii;h and division with- 

 out loss of their specific character. The second 

 assvmiption is that the gemmules are cell-germs 

 originally produced by the somatic cells; and by 

 this Darwin sought to explain the transmission 

 of somatogenic or acquired characters. How 

 have these two assumptions fared with the prog- 

 ress of modern studies on the cells ? ' 



' The development of the gemmules was supposed to depend on 

 their " union with other partially developed or nascent cells, which 

 precede them in the regular course of growth." Darwin does 

 not make it quite clear whether he assumed that the gemmules 

 actually grow into new cells. Many passages (like the one placed 

 in quotation marks in the text above) seem open to no other 

 interpretation; but in the case of plants, accepting the universality 

 of division in them, he concluded that "the gemmules derived 

 from the foreign pollen do not become developed into new and 

 separate cells, but penetrate and modify the nascent cells of 

 the mother plant." This process, he says, is almost identical with 

 a fertilization of the cells of the mother plant by gemmules 

 derived from the foreign pollen. 



