Obituary. ' 9 



a succession of essays on heredity and other problems, such as 

 length of life, the immortality of the Protozoa, death, the signifi- 

 cance of sexual reproduction. These excited great interest and 

 stimulated research and enquiry. His studies on the Hydrozoa led 

 him to the important idea of the continuity of the germ plasm, 

 which has passed into the body of biological doctrine as a general 

 explanation of the everyday fact that like tends to beget like. 



From the idea of the continuity of the germ-plasm, Weismann 

 worked logically onwards towards two great results — on the one 

 hand, the elaboration of a hypothetical picture of the organization 

 of the physical basis of inheritance (expressed in his famous 

 " Germ Plasm ") ; and, on the other hand, the destructive criticism 

 of the evidence on which had rested the widespread belief in the 

 transmission of somatic modifications' (structural changes acquired 

 in the lifetime of an individual organism as the direct result of 

 peculiarities in environment and function). His idea of con- 

 stituents in the germ-plasm corresponding to every independently 

 variable and independently heritable character has been continued 

 into the more recent conceptions of germinal factors, determiners, 

 or genes corresponding to the unit characters of the Mendelians 

 and Mutationists. His scepticism as to the transmission of indi- 

 vidually acquired modifications has had a great influence and has 

 prompted some very important investigations and not a little 

 careful thinking. Perhaps the most characteristic expression of 

 Weismann's mind is the hypothesis of germinal selection, by which 

 he sought to account for detmiteness in variation, for it illustrates 

 his resolute power of following an idea to its logical consequences. 

 He adhered with the strongest conviction to the Darwinian view 

 of the importance of selection as a directive factor in evolution, 

 but he widened and deepened the doctrine with clearness and ' 

 subtlety. Many biologists of to-day are far from accepting 

 ' Weismannism." but we are all agreed in recognizing the stimu- 

 lating influence which he has exerted, and in admiring the nobility 

 and sincerity of his life and work. 



J. A. T. 



