102 FACTOES OF EVOLUTION 



now approaches a step nearer to that ultimate distribution of polar 

 forces which exists in the adult organism, are coerced more 

 directly into the typical structure. Thus there is necessitated a 

 series of compromises. Each successive form assumed is unstable 

 and transitional : approach to the typical structure going on hand 

 in hand with approach to the typical bulk." 



This may seem very complicated ; but it appears to be a 

 condition inseparable from all attempts to explain organisation 

 and heredity. What has to be steadily borne in mind is the fact 

 that this hypothesis is quite in accord with all the known data 

 as to regeneration and repair in animals ; as well as with the 

 phenomena of reproduction by buds, cuttings, and superficial 

 scales in plants, to which reference has previously been made 

 (pp. 89-91) ; while Weismann's counter hypothesis concerning 

 ' ids ' and ' determinants ' utterly fails to give any rational 

 account of such phenomena. 



And now it seems clear that what Spencer says in this last 

 quotation may help us to understand the possibility of the occur- 

 rence from time to time of what are known as 'sports,' arising 

 during the development of plants and animals — such as have been 

 long known to occur and have been habitually taken advantage 

 of by breeders in their efforts to establish new races or new 

 varieties. The occurrence of such sports has in recent years 

 been much dwelt upon by Hugo de Vries' in the foundation of 

 his doctrine of the origin of species by 'Mutation,' as also by 

 W. Bateson in his work on ' Discontinuous Variation.' 



Just as in a gemma or egg of one of the lower organisms when 

 subjected to unnatural conditions, isomeric changes in the living 

 substance may be brought about, leading to the production of an 

 entirely different form of life (Heterogenesis), so, it seems to me, 

 we must look to some isomeric changes occurring in particular 

 parts of the living substance of a plant or animal, during some of 

 its later developmental phases, in order to account for the occur- 

 rence of ' sports ' and perhaps for the origin of new species by 

 ' Mutation,' after the manner made known by de Vries. 



The investigations of this latter distinguished worker have, 

 indeed, cast quite a new light upon the importance of this subject 

 and, together with the researches of Neo-Lamarckians, seem to 

 necessitate a readjustment of our notions as to the range of action 

 and as to the modus operandi of ' natural selection.' 

 ' " Die Mutationstheorie," Leipzig, igoi. 



