Vlll PREFACE. 



when suggesting the origin of nectaries and irregu- 

 larities of flowers in my paper on " Self-fertilisation of 

 Flowers." * 



In 1880, Mr. A. R. Wallace reviewed Dr. Aug. Weis- 

 mann's " Studies in the Theory of Descent." f In this 

 work the author says : " According to my view, trans- 

 mutation by purely internal causes is not to be enter- 

 tained. . . . The action of external inciting causes is 

 alone able to produce modifications." Mr. Wallace adds 

 that he had "arrived at almost exactly similar con- 

 clusions." 



In 1881, when reviewing Paul Janet's work on 

 " Final Causes," J I took occasion to remark that " I 

 regarded the environment as by far the most important 

 "cause" of variations, in that it influences the organ- 

 ism, which, by its inherent but latent power to vary, 

 responds to the external stimulus, and then varies 

 accordingly." 



In 1881, appeared the first really systematic treatise 

 that I know of, by Dr. C. Semper, § which dealt with the 

 oriorin of variations in animals as beino^ referable to the 

 environment. 



In 1884, Dr. A. de Bary's "Comparative Anatomy of 

 the Vegetative Organs of the Phanerogams and Ferns," 



* Trans. Lin. Soc, 2nd ser., Bot., vol. i., p. 317. 

 t Nature, xxii., p. 141. X Modern Review, 1881, p. 53. 



§ The Natural Conditions of Existence as they affect AnimalSy" Intern. 

 Sci. Ser., vol. xxxi. 



