15 

 16 

 17 

 18 

 19 

 20 



362 DARWINISM TO-DAY. 



(3) tendency, when much disturbed, to revert from a sub-type to 

 an earlier form; (4) occasional sports which may give rise to new 

 types." 



10 Emery, C, "Gedanken zur Descendenz- und Vererbungstheorie," 

 Biolog. Ccntralbl, Vol. XIII, pp. 397-420, 1893. 



11 Korschinsky, S., "Heterogenesis und Evolution," Naturw. 

 Wochenscrift, Vol. XIV, pp. 273-278, 1899; also ''Heterogenesis u. 

 Evolution," Flora, odcr Allg. Bot. Zcit., Erganzungsbd. 89, pp. 240- 

 368, 1901. 



12 De Vries, H., "Die Mutationstheorie," Vol. I, 1901, Vol. II, 

 1903. 



References to ' De Vries R > " S P ecie s and Varieties, Their 



discussions by Origin by Mutation" (ed. by MacDougal), 1905. 



de Vries of spe- 14 De Vries, H., "Die Mutationstheorie," Vol. I, 

 .cies-forming. p I5O> igQI 



De Vries, H., "Die Mutationstheorie, Vol. I. p. 362, 1901. 



De Vries, H., "Species and Varieties," p. 6. 



De Vries, H., "Species and Varieties," pp. 8-9. 



De Vries, H., "Species and Varieties," p. 10. 



De Vries, H., "Species and Varieties," p. 13. 



For an excellent exposition and discussion of the de Vries muta- 

 tion theory and mutations, see Lotsy, J. P., "Vorlesungen iiber De- 

 scendenztheorien," Vol. I, chaps, xiv and xv, 1906. 



21 Morgan, T. H.. "Evolution and Adaptation," pp. 294-295, 1903. 



22 As evidence of the interest and favour with which American 

 biologists have received the theory, the six addresses on "the muta- 



American ^ on tneorv f organic evolution" delivered before the 



opinion of the American Society of Naturalists at Philadelphia, 

 mntations December 28, 1904. may be especially referred to. 



theory, These addresses by naturalists distinguished for their 



work in different phases of biology, as systematic and cecologic 

 botany, cytology, human anatomy, animal cecology, etc., are printed 

 in ^Scicnce, N. S., Vol. XXI, pp. 521-543 (April 7, 1905), and from 

 them I quote various paragraphs indicating some of the points 

 of view of the speakers and some of the arguments advanced in 

 favour of the theory. 



"On the whole, it appears that the formation of new breeds be- 

 gins with the discovery of an exceptional individual, or with the 

 production of such an individual by means of cross-breeding. Such 

 exceptional individuals are mutations" (Castle, p. 524). 



"Modification of character by selection, when sharply alternative 

 conditions (i. e., mutations) are not present in the stock, is an 

 exceeding difficult and slow process, and its results of questionable 

 permanency. Even in so-called 'improved' breeds, which are sup- 



