2IO BIOLOGICAL LECTURES. 



the problem of development presents itself in the form of an 

 alternative — one choice between two contradictory extremes. 

 It is epigenesis or evolution, with no middle ground for 

 Bourne, and with only a minimum for Hertwig. Hertwig 

 accepts determinants in homoeopathic doses — just enough to 

 fix the characters of individual cells, but not enough to affect 

 cell-complexes.^ Bourne, with fully as much loyalty to epi- 

 genesis as to "fact," holds that the truth lies on the side of 

 epigenesis, and epigenesis, be it noted, as understood by 

 Harvey and Wolff. As Bourne echoes prevalent sentiment in 

 a somewhat emphatic form, it may be well to note his words : 



"The subsequent history of the oosperm," he says, "that 

 is, of the ovum after it is impregnated, is an absoliUe demon- 

 stration of epige7iesis in the sejise in zvhich it zvas understood by 

 Harvey and Caspar Friedrich Wolff.'" Notwithstanding this 

 high degree of certainty, we are told that " there is some 

 reason to fear that, unless a protest is raised, the failure of the 

 attempts to form hypotheses explaining the causes of develop- 

 mental phenomena, on epigenetic grounds [no pretension .^] will 

 discredit the doctrine of epigenesis as a statemejit of the observed 

 facts of development.'' 



There is no doubt some danger that " the doctrine of 

 epigenesis," as understood by Harvey and Wolff, can hardly 

 be accepted even as a statement of the "facts" of develop- 

 ment. But facts easy of "absolute demonstration" are fairly 

 safe, however much the epigenesis of past centuries may have 

 to be revised in order to accord with the results of recent 

 work. 



Mr. Bourne's criticisms ^ of what he calls evolutionary views 

 do not concern us here further than as they reflect current 

 misconceptions, which tend to obscure fundamental principles. 



1 Herbert Spencer (IVeistnajiiiistn Once More, Postcript, p. 24) exposes the 

 weak point in a single remark : " To this it may be replied that the ability to form 

 the appropriate cell-cotnplexes, itself depetids upon the constitutional iinits contained 

 in the cells.'" " Constitutional units " Mr. Spencer offers as a substitute for 

 "physiological units." 



2 Those directed against " The Inadequacy of the Cell-theory of Develop- 

 ment " are largely the result of misunderstanding, which may be trusted to cor- 

 rect itself. 



