vi OBITUARY NOTICES OF MEMBERS DECEASED. 



Weismann's contributions to biological theory were so extensive 

 and important that they overshadow to a great extent his observa- 

 tional and experimental work, and yet the latter was by no means 

 small or unimportant. Among these observational and experimental 

 studies must be mentioned especially his extensive works on " The 

 Development of Diptera (1865)," "Natural History of the Daph- 

 noidea" (1876-79), "Origin of the Sex Cells of the Hydromedus^ 

 (1883)," "Seasonal Dimorphism of Butterflies" (1875), "Origin 

 of Z\Iarkings of Caterpillars" (1876) and "Transformation of the 

 Mexican Axolotl into Amblystoma." 



Some of his earlier work was done without assistance, but in all 

 of his later observational and experimental studies he had the as- 

 sistance of his wife or other helpers. Much of his work was done 

 in collaboration with some of his students or assistants. His method 

 of work was to a large extent forced upon him by his eye affliction. 

 After 1864 all reading had to be done for him, at first by his wife 

 and after her death by a secretary. Experimental work was done 

 under his supervision by his assistant and janitor. All microscopic 

 work was done by his pupils, to whom he suggested topics and 

 Avhose work he supervised daily. These theses were always in 

 direct relation to his theories and to that phase of them which in- 

 terested him most at the moment. 



But valuable as much of his observational and experimental 

 work was, there is no doubt that he will be remembered chiefly for 

 his theories of heredity. His earliest writings on this subject date 

 from the year 1883 and his latest were pubHshed but a few years 

 before his death. His "Essays upon Heredity and Kindred Bio- 

 logical Topics " were translated into English and published in two 

 volumes in 1889 and 1892. Probably his most important work on 

 this subject is his book entitled "The Germ-Plasm, A Theory of 

 Hereditv" which was published in EngHsh in 1893. Subsequent 

 worKs ^.. Heredity are "On Germinal Selection" (1896) and " Vor- 

 trage iiber Descendenztheorie " (1902). This last-named work, 

 which was pubhshed in English under the title "The Evolution 

 Theory" (1904), consists of a summary and an expansion of many 

 of his previous writings on the subjects of evolution and heredity; 



