96 



THE GERM -PLASM 



the truth cannot be decided by a consensus of opinion, it is 

 nevertheless a significant fact that the views of such naturahsts 

 as Rav Lankester.* Thisehon Dver, Brooks, Mevnert.t van 

 Bemmelen.l and others, coincide with my own. 



The fact, however, that we deny the transmission of the effects 

 of use and disuse, does not imply that these factors are of no im- 

 ])ortance : and I have already attempted to show in former essays 

 that both use and disuse may lead indirectly to variations, — the 

 former wherever an increase as regards the character concerned 

 is useful, and the latter in all cases in which an organ is no 

 longer of any importance in the preservation of the species, and 

 in which, so far as the disused organ is concerned, 'panmixia' 

 occurs. 



Want of space prevents me from discussing these questions 

 in detail ; their consideration belongs rather to a work on the 

 theory of descent than to one on that of heredity, and I need 

 only refer to my former essays,§ in which. I think, sufficient 

 proof is given to show that the gradual degeneration of organs 

 which are no longer of use does not require the assumption of 

 the transmission of somatogenic variations, and that conse- 

 quently the facts do not compel us to adopt a hypothesis which 

 we seem unable to accept theoretically. 



It therefore remains to be seen whether w^e are not acquainted 

 with other facts which are explicable only on such a hypothesis : 

 one side of this question will now be treated of in particular. 



2. The Hypothesis Tested by Facts 



A few words will suffice concerning the hypothesis of the 

 transmission of injuries and vuiiilations, which has been accepted 

 for so long a time, and is obstinately defended even at the 

 present day ; for since the appearance of my essay on ' The 



* Ray Lankester, 'The History and Scope of Zoology,' ' Enc. Brit.,' 

 Vol. xxiv. 



t Meynert, ' Mechanik der Pliysionomik,' a Lecture held at the Meeting 

 of German Naturalists at Wiesbaden, 1887. 



X J. F. van Bemmelen, ' De Erfelijkheid van verwooven Eigenschappen,' 

 s'Gravenhage, 1890. 



\J Cf., ' Uber die Verebung,' Jena, 1883, and ' Die Continuitat des 

 Keimplasma's als Grundlage einer Theorie der Verebung,' Jena, 1885. 

 English translation, ' Essays upon Heredity,' pp. 71 and 165. 



