STUDIES IN SPERMATOGENESIS. II. 



A COMPARATIVE STUDY OF THE HETEROCHROMOSOMES IN CERTAIN SPECIES 



OF COLEOPTERA, HEMIPTERA, AND LEPIDOPTERA, WITH ESPECIAL 



REFERENCE TO SEX DETERMINATION. 



By N. M. STEVENS. 



INTRODUCTION. 



In Part I of this series of papers, the spermatogenesis of five species 

 belonging to four different orders ol insects was considered. In two 

 species of Orthoptera an ' ' accessory chromosome ' ' was found ; in 

 Tenebrio molitor, one of the Coleoptera, an unequal pair of chromo- 

 somes was described ; in the other species no heterochromosomes were 

 discovered. The apparent bearing of the chromosome conditions in 

 Tenebrio molitor on the problem of sex determination has led to a 

 further investigation of the germ cells of the Coleoptera. One of the 

 Hemiptera homoptera and two of the Lepidoptera have also been 

 examined for comparison with the Coleoptera and the Hemiptera 

 heteroptera. 



METHODS. 



As a result of previous experience with similar material, only two 

 general methods of fixing and staining have been employed: (i) Fix- 

 ation in Flemming's strong solution or Hermann's platino-aceto-osmic, 

 followed by either Heidenhain's iron-haematoxylin or Hermann's 

 safranin-gentian staining method (Arch. f. mikr. Anat. 1889). (2) 

 Fixation after Gilson's mercuro-nitric formula, followed by iron- 

 hsematoxylin, Delafield's hsematoxylin and orange G, Auerbach's 

 combination of methyl green and acid fuchsin, or thionin. 



The iron-hsematoxylin with either mode of fixation gives by far the 

 most satisfactory preparations for general study. The other stains 

 were used mainly for the purpose of distinguishing between hetero- 

 chromosomes and plasmosomes in resting stages of the nucleus. 



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DEC 22 1915 



