STUDIES ON CHROMOSOMES 



V THE CHROMOSOMES OF METAPODIUS. A CONTRI- 

 BUTION TO THE HYPOTHESIS OF THE GENETIC 

 CONTINUITY OF CHROMOSOMES 1 



BY 



EDMUND B. WILSON 

 WITH ONE PLATE AND THIRTEEN FIGURES IN THE TEXT 



The genus Metapodius (Acanthocephala), one of the coreid 

 Hemiptera, shows a very exceptional and at first sight puzzling 

 relation of the chromosome-groups which has seemed to me worthy 

 of attentive study by reason of its significance for the hypothesis 

 of .the "individuality" or genetic continuity of the chromosomes. 

 The most conspicuous departure from the relations- to which we 

 have become accustomed lies in the fact that different individuals 

 of the same species often possess different numbers of chromo- 

 somes, though the number in each individual is constant. An 

 even more surprising fact is that in all of my own material every 

 male individual possesses at least 22 spermatogonial chromosomes, 

 including a pair of unequal idiochromosomes like those of the 

 Pentatomidae, while in Montgomery's material of M. terminalis 

 every male has but 21 spermatogonial chromosomes, one of which 

 is a typical odd or "accessory" chromosome (unpaired idiochro- 

 mosome). 2 



The present paper presents the results of an investigation of 

 these relations that has now extended over nearly four years, in 

 the course of which serial sections of more than sixty individuals 



1 Part of the cost of collecting and preparing the material for this research was defrayed from a grant 

 of $500 from the Carnegie Institution of Washington, made in 1906. I am indebted to Rev. A. H. 

 Manee, of Southern Pines, N. C., for valuable cooperation in the collection of material, and to Dr. 

 Uhler, Mr. Heidemann, Mr. Van Duzee, and Mr. Barber for aid in its identification. 



2 By Professor Montgomery's courtesy I have been enabled to study thoroughly his original prep- 

 arations and to satisfy myself of the correctness of his account (Montgomery '06). I also owe to him 

 a number of unsectioned testes of the same type. 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. vi, NO. 2. 



