STUDIES IN SPERMATOGENESIS WITH ESPECIAL REF- 

 ERENCE 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 chromo- 

 some," which, according to McClung ('02), may be a sex determinant. 

 This view has been supported by Button ('02) in his work on Brachy- 

 stola magnet, 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 (i) a California termite, Termopsis 

 angusticollis ; (2) a California sand-cricket, Stenopelmatus ; (3) the 

 croton-bug, Blatlella germanica ; (4) the common meal-worm, Tene- 

 brio molitor ; and (5) one of the aphids, Aphis cenothercz. 



A brief account of a chromatin element resembling the accessory 

 chromosome in Sagitta has been added for comparison. The spermato- 

 genesis 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 excel- 

 lent fixation and were preferable to the osmic mixtures when it was 

 desirable to stain the same material with iron-hsematoxylin, and also 

 with various anilin stains. 



Heidenhain's iron-haematoxylin, either alone or with orange G 

 or erythrosin, was used more than any other one stain. With osmic 

 fixation safranin gave better results in some cases, because of the 



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