STUDIES ON CHROMOSOMES. 



I. THE BEHAVIOR OF THE IDIOCHROMOSO.MES IN 



HEMIPTERA. 1 



EDMUND B. WILSON. 



WITH 7 FIGURES. 



In studying the spermatocyte-divisions in Lygaeus turcicus and 

 Coenus delius, and afterward in several other genera of Hemip- 

 tera, my attention was directed to the fact that the number of 

 chromosomes appeared to vary, polar views of the equatorial 

 plate showing sometimes seven chromosomes," sometimes eight 

 (cf. Figs. ib y it, 2a, 2i, 3</, 3/, etc.). Montgomery, iritis fe^nsive 

 comparative paper of 1901, describes and figures a similar' Varia- 

 tion in a number of cases, including Coenus delius and Euschistus 

 tristigmus ('01, I, pp. 161, 166), and in the latter case considered 

 it as a result of variations in the synapsis of the two "chromatin 

 nucleoli" which he supposed might either conjugate to form a 

 bivalent body before the first division (in which case this division 



'This paper is based on a study of some very fine series of sections of the testes of certain Hemiptera, 

 prepared six or eight years ago by Dr. F. C. Paulmier, in connection with his valuable paper on the 

 spermatogenesis of Anasa tristis ('99). Part of the original Anasa sections, with a number of series of 

 the testes of some other insects, were given to the cytological cabinet of the Columbia laboratory at that 

 time; some of the best of the remainder were subsequently loaned to Mr.Sutton, and others to Dr. Dublin, 

 for comparison with their work on the spermatogenesis of other forms. Certain inconsistencies in the 

 literature relating to the accessory chromosome and the microchromosomes or "chromatin-nucleoli " 

 led me to re-examine the preparations of Anasa and some of the other genera, which yielded some new 

 and interesting conclusions in the case of Anasa, and also of Alydus, Lygaeus and Ccenus. Dr. Paulmier 

 being preoccupied with other lines of work did not find it practicable again to take up his cytological 

 studies, and he was generous enough to give me, for the laboratory, his entire set of preparations, com- 

 prising, in addition to the slides already given or loaned, serial sections of more than a hundred testes 

 representing upward of twenty genera of Hemiptera and other insects. A typical series of the Hemip- 

 tera from which these testes were taken had been identified by the eminent specialist, Mr. P. R. Uhler. 

 Much of this material is admirably fixed, sectioned and stained, and the best preparations are a model of 

 technical excellence, showing especially the chromosomes of the spermatogonial and spermatocyte 

 divisions with a clearness and brilliancy comparable with that of the best Ascaris preparations. The 



