Ortmann.] J-^^ [May 15, 



it is now demonstrated by the ablest scientists explicitly,* and by many 

 olliers incidentally, that his theories are without any proper foundation. 

 As regards Eimer's theories, I have endeavored in the above to show, 

 that the alleged opposition in certain points to Darwin does not exist, 

 except as Eimer creates new scientific terms for old ideas, and as he does 

 not distinguish properly between cause and effect. 



To sum up, we have to d'lsiingnMi four factor s\ accomplishing the diver- 

 sity, developracLt and differentiation into species of organic beings : we 

 may call conveniently this whole process : origin of species. 



1. All organic beings vary. There exists an "inherent tendency to 

 vary,":}: but this tendency is manifested only by the influence of external 

 causes upon the respective organism. The faculty of variation is an 

 unlimited one,§ but the actual variation is limited, namely by the external 

 conditions of life. Variations coming into existence are modifications 

 " directly due to the physical conditions of life," which "in this sense 

 are supposed not to be inherited. "|| ^1 variation is impossible without 

 external conditions producing it. 



2. These variations may be transmitted to descendants.^ Inheritance is 

 due to the process of propagation, which may be either by one parent or 

 by two parents (Amphimixis). By inheritance acquired ciiaracters are 

 transmitted from the parent to the descendants, and thus the consangu- 

 inity becomes morphologically visible, and individuals of common descent 

 are more closely connected by morphological characters with each other 

 than with any other group of individuals. By inheritance the unsteady 

 and temporary variations are transformed into varieties, that is to say, 

 into groups of individuals having the same ancestors and resembling each 

 other more or less.** 



*I refer to the followiug names : Eimer, Haacke, Haeckel, O. Hertwig, Pfeffer, Romanes, 

 Spencer, and others. I would especially mention O. Hertwig's book, Zeil- und Streit-Fragen 

 tier Biologie, Heft i, " Praeformation oder Epigenesis." I recommend this masterjoiece of 

 criticism for study, not only because it refutes completely Weismann's fantastic germ-plasma 

 theory, but because the exposition of this theory given in that work is much more intelli- 

 gible than that given by Weismann himself. In his latest paper ("Germinal Selection," 

 pp. 282, 285 and 286) Weismann refers to Hertwig's criticism : but his remarks are entirely 

 aside from the question, since they do not touch the chief point, and, partly (p. 282), attri- 

 bute to Hertwig an opinion which the latter, according to his own express statement, did 

 not entertain (see pp. 10 and 11 of Hertwig's book). 



fSee Crrundziige, etc., p. 32. 



J Darwin, Var. and Domes., p. 2. 



? Unless checked by inheritance ! 



II Darwin, Orig., p. 33. 



1[ The transmission of acquired characters is denied by many competent naturalists and 

 cannot be regarded as demonstrated. In the problems of geographical distribution one is con- 

 tinually brought back to this as a probable assumption, and I propound it here as a " work- 

 ing hypothesis." 



=** Darwin, Orig., p. 33: In "the term variety .... community of descent is ... . im- 

 plied." 



