STUDIES ON CHROMOSOMES. 



II. THE PAIRED MICROCHROMOSOMES, IDIOCHRO- 

 MOSOMES AND HETEROTROPIC CHRO- 

 MOSOMES IN HEMIPTERA. 1 



BY 



EDMUND B. WILSON. 

 WITH 4 FIGURES. 



In investigating the physiological significance of the chro- 

 mosomes and their individual values in heredity, it is important 

 to determine as accurately as possible how far they are differen- 

 tiated in respect to individual behavior, and to ascertain by the 

 comparative study of different forms to what extent the chro- 

 mosomes can be grouped in well-defined classes. The work of 

 Henking, Paulmier, Montgomery, Gross and Stevens on the Hemip- 

 tera has shown that this group is peculiarly favorable for such a 

 study; and I believe from my own observation that no group of 

 animals has thus far been examined that offers greater advan- 

 tages in this direction. 2 But although the general results obtained 

 by the above-mentioned observers are of great value and interest 

 they nevertheless show many discordances of detail that stand in 

 the way of a consistent general interpretation of the phenomena, 

 while some of Gross's conclusions are a stumbling block in the 

 way of the whole theory of the individuality of the chromosomes. 

 For this reason I propose in this paper to record a series of obser- 

 vations that I hope may serve to clear away some of the con- 

 fusion that now exists in the accounts of the subject, and that 

 open the way, I believe, to a true interpretation of the "accessory 

 chromosome" and its relation to the determination of sex. 



In a series of suggestive papers ('01, '04, '05) Montgomery 



'Attention is called to the Appendix in which are briefly recorded facts, determined by later 

 observations, that exactly realize the theoretic expectation regarding the sexual differences of the 

 chromosome-groups, stated at p. 539. An abstract of these observations was published in the issue of 

 Science for Oct. 20, 1905. 



2 J am much indebted to Mr. Uhler's kindness in identifying many of the species examined. 



