CHAPTER IX 



Symbionticism in Relation to Heredity and 

 Development 



When Darwin advanced his theory on the origin of 

 species, there was practically nothing known concerning 

 the mechanism of heredity or the factors concerned in 

 development. Darwin felt the need of an hypothesis that 

 would explain the operations of heredity, and advanced 

 his own theory of ''pangenesis" to fill this gap. The situa- 

 tion is quite different today; instead of formulating a new 

 theory of heredity to fit our ideas as to the origin of species, 

 it becomes necessary to fit the conception of Symbionticism 

 to a more or less established mechanism of heredity. 



Since the rediscovery, in 1900, of Mendel's researches 

 there has grown up an extensive Uterature on the nature of 

 the factors of heredity. It becomes necessary to hmit our 

 discussion to the generahzations and analyses that have 

 been made in reviews on genetics and cytology. We are 

 especially indebted to Wilson's comprehensive treatise: 

 "The Cell in Development and Heredity" ('25) ; to Morgan, 

 Sturtevant, Muller, and Bridges ('15) for ''The Mechanism 

 of MendeUan Heredity;" and to Conkhn for an analytic 

 review of the researches in heredity, dehvered as a series 

 of lectures under the WiUiam Ellery Hale foundation and 

 pubhshed in the Scientific Monthly ('19-'20). Space does 

 not permit an extensive review of the data that have been 

 brought forth in these books and papers. We prefer to 

 discuss some of those features of heredity and development 

 that appear to have a direct bearing upon the theory of 

 Symbionticism. 



Certain difficulties are encountered in the use of some of 



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