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 WITH ESPECIAL REFERENCE TO THE "ACCESSORY CHROMOSOME" BY N. M. STEVENS. [Illustration] WASHINGTON, D. C.: Published by the Carnegie Institution of Washington September, 1905. CARNEGIE INSTITUTION OF WASHINGTON PUBLICATION No. 36 FROM THE PRESS OF THE HENRY E. WILKENS PRINTING CO. WASHINGTON, D. C. STUDIES IN SPERMATOGENESIS WITH ESPECIAL REFERENCE TO THE "ACCESSORY CHROMOSOME." By N. M. STEVENS. In connection with the problem of sex determination it has seemed necessary to investigate further the so-called "accessory chromosome," which, according to McClung ('02), may be a sex determinant. This view has been supported by Sutton ('02) in his work on _Brachystola magna_, but rejected by Miss Wallace ('05) for the spider. The forms selected for study have been taken from several groups of insects, and are all species whose spermatogenesis has not been previously worked out. They are (1) a California termite, _Termopsis angusticollis_; (2) a California sand-cricket, _Stenopelmatus_; (3) the croton-bug, _Blattella germanica_; (4) the common meal-worm, _Tenebrio molitor_; and (5) one of the aphids, _Aphis oenotherae_. A brief account of a chromatin element resembling the accessory chromosome in _Sagitta_ has been added for comparison. The spermatogenesis of each form will be described in detail, and a general discussion of the results and their relation to the accessory chromosome and sex determination will follow. The spermatogenesis of the aphid has been included in another paper, but a summary of results and a few figures will be given here for reference in the general discussion. METHODS. The testes were fixed in various fluids--Flemming's strong solution, Hermann's platino-aceto-osmic, Gilson's mercuro-nitric, Lenhossek's alcoholic sublimate acetic, and corrosive acetic. Flemming's and Hermann's fluids followed by safranin gave good results in most cases. The mercuro-nitric solution and Lenhossek's fluid gave excellent fixation and were preferable to the osmic mixtures when it was desirable to stain the same material with iron-haematoxylin, and also with various anilin stains.