52 THE PLAY OF ANIMALS. 



Eimer,* Wilser^f Hertwig^ Eomanes,** Herbert Spen- 

 cer,! | Wundt,^ Siilly^O and Eibot.1; The truth is, it is 

 not yet given to ns entirely complete, for almost every 

 work of the gifted author yet published shows some 

 modification more or less important.:!; The weightiest 

 point to be determined before the theory can be further 

 developed is that of the relation of the individual to the 

 hereditary substance or of the soma to the germ plasm. 

 Does this germ plasm pervade the endless series of in- 

 dividuals with absolute continuity, changing only 

 through its combination with that of other individuals 

 (amphimixis)? Weismann formerly appeared to attrib- 

 ute absolute persistence to the germ plasm; indeed, 

 he has, in one instance at least, emphasized this doctrine. 

 Yet in 1886 he admitted that monads that are propa- 

 gated by mere division may inherit acquired characters. J 

 In 1891 he limits this possibility to unicellular structures 

 without a nucleus.** In other directions, however, he has 



* Th. Eimer, Die Eiitstehung der Arten aiif Grund von Verer- 

 ben erworbener Eigensehaften nach den Gesetzen organischen 

 Wachsens, 1888. 



f L. Wilser, Die Vererbung der geistigen Eigenschaften, 1892. 

 X O. Hertwig. Zeit- und Streitfragen der Biologic, vol. i. Pra- 

 formation oder Epigenese?, 1894. 



* G. J. Romanes, Critical Examination of Weismannism. 



II Herbert Spencer, The Inadequacy of Natural Selection, 1803. 

 A Rejoinder to Professor Weismann, 1803. Weismannism once 

 more, 1894. 



^ Wundt, Vorlesungen iiber die Menschen- und Thierseele, sec- 

 ond edition, 1802, p. 441. 



J. Sully, The Human Mind, 1802, i, p. 139. 



:l Th. Ribot, L'heredite psychologique, 1894. preface. 



^ Since this was written the theory of " Germinal Selection " 

 has been added to it. 



J Die Bedeutung der sexuellen Fortpflanzung fiir die Selec- 

 tionstheorie, Jena, 1886, p. 38. 



*"^ Amphimixis, Jena, 1891. (Weismann must of course hold to 



