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 œnotheræ.
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.