Produced by Bryan Ness, Josephine Paolucci and the Online Distributed Proofreading Team at https://www.pgdp.net. (This file was produced from images generously made available by The Internet Archive/American Libraries.) STUDIES IN SPERMATOGENESIS PART II. (PAGES 33-74. PLATES VIII-XV.) A COMPARATIVE STUDY OF THE HETEROCHROMOSOMES IN CERTAIN SPECIES OF COLEOPTERA, HEMIPTERA AND LEPIDOPTERA, WITH ESPECIAL REFERENCE TO SEX DETERMINATION. BY N. M. STEVENS [Illustration] WASHINGTON, D. C.: Published by the Carnegie Institution of Washington October, 1906 CARNEGIE INSTITUTION OF WASHINGTON PUBLICATION NO. 36, PART II. FROM THE PRESS OF THE WILKENS-SHEIRY PRINTING CO. WASHINGTON, D. C. 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 of insects was considered. In two species of Orthoptera an "accessory chromosome" was found; in _Tenebrio molitor_, one of the Coleoptera, an unequal pair of chromosomes 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: (1) Fixation in Flemming's strong solution or Hermann's platino-aceto-osmic, followed by either Heidenhain's iron-hæmatoxylin or Hermann's safranin-gentian staining method (Arch. f. mikr. Anat. 1889). (2) Fixation after Gilson's mercuro-nitric formula, followed by iron-hæmatoxylin, Delafield's hæmatoxylin and orange G, Auerbach's combination of methyl green and acid fuchsin, or thionin. The iron-hæmatoxylin 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 heterochromosomes and plasmosomes in resting stages of the nucleus. COLEOPTERA. Trirhabda virgata (Family Chrysomelidæ). Two species of _Trirhabda_ were found in larval, pupal, and adult stage on _Solidago sempervirens_, one at Harpswell, Maine, the other at Woods Hole, Massachusetts. The adult insects of the two species differ slightly in size and color, the germ cells mainly in the number of chromosomes, _Trirhabda virgata_ having 28 and _Trirhabda canadense_ 30 in spermatogonia and somatic cells.