THE CHROMOSOMES IN DIABROTICA VITTATA, 

 DIABROTICA SOROR AND DIABROTICA 12-PUNC- 

 TATA 



A CONTRIBUTION TO THE LITERATURE ON HETEROCHROMO- 

 SOMES AND SEX DETERMINATION 



BY 



N. M. STEVENS 

 With Three Plates 



In Publication No. 36 of the Carnegie Institution of Washington, 

 the spermatogenesis of a number of Coleoptera was described, 

 and discussed with reference to the determination of sex. The 

 study of the Diabroticas was begun at Cold Spring Harbor in the 

 summer of 1906, and I wish to express my gratitude to Dr. C. B. 

 Davenport for the privileges granted me both at the Carnegie 

 Institution for Experimental Evolution and in the research labora- 

 tory of the Brooklyn Institute. I am also much indebted to Miss 

 Isabel McCracken of Stanford University for material of Dia- 

 brotica soror, prepared with the greatest care and sent to me in 

 December, 1906, and March, 1907. 



The same methods were used as in previous work on the germ 

 cells of the Coleoptera. The germ glands were fixed in Gilson's 

 mercuro-nitric fluid, in Flemming's strong chromo-aceto-osmic 

 solution, and in Hermann's platino-aceto-osmic fluid. Sections 5/1 

 thick were stained with iron haematoxylin or with thionin. The 

 aceto-carmine method was used for long series of Diabrotica soror 

 and Diabrotica 12-punctata. 



DIABROTICA VITTATA 



In the majority of the Coleoptera previously studied (85.7 per 

 cent), an unequal pair of heterochromosomes was found. The 

 Diabroticas have an odd or unpaired heterochromosome, resem- 



The Journal of Experimental Zoology, vol. v, no. 4 



