1896.] 187 [Ortmann. 



species of the Derapod genus Gelasiinus on the East African coast 

 recorded by me.* These four species lived in a particular locality com- 

 pletely separated, although often only a few yards from each other, and 

 a collector less careful would have put them all together in one jar. Yet 

 as a rule collectors are well acquainted with the fact that particular spe- 

 cies are to be sought for in particular localities. 



IV. I may, I think, conclude. I have amply demonstrated that only 

 separation can effect differentiation of sp«cies, and that all the principles 

 created by other authors for this particular effect come under the head of 

 separation, i. e , the breaking up of a number of individuals into groups, 

 each subject to particular conditions of life. Some authors, indeed, 

 have not understood at all that the whole process ending in the formation 

 of species is composed of a series of distinct factors, only the last of 

 which is separation. But I wish to say here expressly that already Darwin 

 conceived those different factors correctly, and distinguished them well 

 according to their particular line of action. The only change of Darwin's 

 views that I should like to propose is to substitute for his " principle of 

 divergence" that of "separation." Besides, it would be well to con- 

 ceive the terra "Natural Selection" in a modified sense, as Pfeffer has 

 proposed, and we have seen that there is some advantage in so doing. 

 And farther, Elmer has pointed out that not all the characters of each 

 animal form are subject to natural selection : there are many which do 

 not bear on utility, but are indifferent in this respect. But since such 

 characters are probably also due to the influence of external conditions, 

 they may be transmitted and may increase, giving origin to a distinct 

 direction of variation, f to a "mutation," which is independent of natu- 

 ral selection, and may be called by Elmer's term "Orthogenesis." 



For the rest, the whole of Darwin's theory stands, and none of those 

 " Darwinists after Darwin " — I venture to say — have been able to weaken 

 any of his ideas in the least degree. Especially Weismann has not, since 



*See Grundzilge, etc., p. 33, footnote. Compare also the following sentences of Petersen 

 {Del Videnskabelige Udbytte af Kanonbaadens Ifauchs Togler, 1893, p. 45.5) : " Each species 

 seems to be distributed according to certain rules, which .... can be brought in relation 

 to one or several .... natural conditions," and (p. 457) : " no species is found everywhere 

 in our seas," and farther : F. Dahl, " Vergleicheude Untersuchuugen Uber die Lebensweise 

 wirbelloser Aasfresser," Silz. Ber. Akad. Wist. Berlin, January, 1896, pp. 29, 30. 



t Already Darwin holds the same opinion and concedes {Origiruof Species, ■p\>. 110,111), 

 that there are variations which appear to be of no service whatever to their possessors. This 

 passage is the more interesting, since he talks of the " laws of growth," which are apparently 

 identical with Elmer's " Gesetzen organischeu Wachsens." Comp. farther, ibid., p. 175: 

 " When from the nature of the organism and of the conditions; uiodiflcations have been 

 induced which are unimportant for the welfare of the species, they may be and appa- 

 rently often have been transmitted .... to numerous .... descendants," and p. 176 : 

 " Morphological differences, which we consider as unimportant .... first appeared .... 

 as fluctuating variations, which sooner or later became constant through the nature of the 

 organism and the surrounding conditions." (In the last jiassage the word I have italicized 

 stands originally as important, but according to the foregoing and following sentences this 

 is no doubt a misprint ) 



PROC. AMER. PHILOS. SOC. XXXV. 151. X. PRINTED SEPT. 4, 1896. 



