VUl 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." t 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,"*[: 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 

 origin of variations in animals as being referable to the 

 environment. 



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

 the Vegetative Organs of the Phanerogams and Ferns," 



* TroTis. Lin. 8oc., 2nd ser., Bot., vol. i., p. 317. 

 t Natwre, xxiL, p. 141. % Modem Review, IflSl, p. 53. 



§ The Natwal Conditione of Existence as they affect Animals," Intern. 

 Sci. Ser., toI. xxxi. 



