Volume VII OCTOBER. 1917 No. 1 



STUDIES OF INHERITANCE AND EVOLUTION 

 IN ORTHOPTERA. 11^ 



By ROBERT K. NABOURS. 

 (With Plates I and II.) 



Due to the efforts of many able and earnest workere the approximate 

 end breeding results in numerous groups of plants and animals may 

 now be predicted. If the ancestry of parents for one generation be 

 known the characters and ratios of a resulting complex progeny may 

 be approximately prognosticated. As well also may the characteristics 

 of parents of unknown ancestry be analyzed by the appearance and 

 ratios of their offspring. Although there is an approach to agreement 

 in the matter of end results one finds wide diversity of judgment 

 regarding the fundamental causes. 



Most, if not all Mendelians consider the proof of the segregation of 

 the germ plasm as an insulated substance in embryonic development 

 adequate. It is considered a fundamental principle that the units con- 

 tributed by two parents separate in the germ cells of the offspring 

 without having had any influence on each other. The ideas of the defi- 

 nite location in the chromosomes of the factoi-s giving rise to characters 

 and explaining Mendelian phenomena by means of the manoeuvres of 

 the chromosomes are thought to be satisfactorily supported by a large 

 body of evidence. (Morgan and students.) On the other hand the 

 idea of the insulation and continuity of the germ plasm as an entity 

 independent of the rest of the organism is seriously questioned. There 

 does not seem to be justification for the attempts to connect particular 

 factors with particular chromosomes or parts of chromosomes, and the 

 factorial hypothesis does not necessarily involve the assumption of 

 factors as distinct entities in the germ. (Child.) These diametrically 

 opposed ideas, each the consequence of extensive constructive experi- 

 mentation and consideration, serve to indicate the difficulties involved 

 in attempts to solve the problems of the mechanism of heredity, or the 

 physiology of heredity, or both. 



1 Contributions from the Zoological Laboratory of the Kansas State Agricultural College 

 and Experiment Station. No. 10. The first instalment was published in the Journal of 

 Genetics, Vol. iii. pp. 141 — 170. 



Journ. of Gen. vii I , 



