8 Proceedings of the Koyal Physical Society. 



those of the adult organism — a mixture of characters due to heredity with 

 others due to environment. In other words, the gamete would be to a certain 

 extent plastic, just as is the individual later on. 



Taking this standpoint, the characters of animals would fall into the 

 following categories : — 



A. Inherited — ■ 



(1) Ancestral; gametic; pne-conjugational. 



(2) Amphimixis ; conjugational. 



B. Environmental — 



(3) Prse-conjugational (i.e., produced by the action of environ- 



mental conditions upon the gametes). 



(4) Conjugational. 



(5) Post-conjugational (i.e., produced by the action of environ- 



mental conditions upon the zygote). 



Apparently new characters — i.e., variations — might obviously belong to 

 any of these categories, except the first. As is well known, Weismann has 

 suggested that those included under (2) are of great importance in Evolution, 

 while he has done the great service of demonstrating how insufficient is 

 the evidence that those included under (5) — "acquired characters" in the 

 ordinary sense — play any part at all in Evolution. As a matter of fact, we 

 cannot be said to have any proof that such characters as would be included 

 in (2) and (4) actually exist in Nature. As regards class (3) our knowledge 

 is still in its infancy, but recent and contemporary work indicates with 

 no uncertain accent that it is there where the causes of the variations which 

 form the basis for evolutionary change are to be sought : 1 it is in fact during 

 the periods before conjugation that the elements of the gonad have impressed 

 upon them these constitutional changes which find their expression in the 

 zygote, and in the individual which develops from it, as variations which 

 tend to be inherited by future generations. No doubt the chief environ- 

 mental impulses acting upon the cells of the gonad, are those which come 

 to them from changes in the metabolism of the parental tissue in which 

 they are developing ; these changes in metabolism being in turn due, some 

 of them, to internal processes in the organism, others to direct influences 

 received from the outer world. 



1 See, e.//., Tower's beautiful paper, "An Investigation of Evolution in Olirysomelid 

 Beetles of the genus Lcptinotarsa." Carnegie Institute, Washington, 1900. 



Agat alflo finds, in the case of ,S7 iiuirrplitiliis, that the. gonad may be influenced by 

 certain external conditions in such a way as to produce eggs which develop into abnormal 

 individuals. The production of such abnormal individuals continues for some time after 

 the removal of the excitina cause. 



