STUDIES IN SPERMATOGENESIS
WITH ESPECIAL REFERENCE TO THE
"ACCESSORY CHROMOSOME"
BY N. M. STEVENS.
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 seemednecessary to investigate further the so-called "accessory chromosome,"which, according to McClung ('02), may be a sex determinant. This viewhas 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 ofinsects, and are all species whose spermatogenesis has not beenpreviously worked out. They are (1) a California termite, Termopsisangusticollis; (2) a California sand-cricket, Stenopelmatus; (3) thecroton-bug, Blattella germanica; (4) the common meal-worm, Tenebriomolitor; and (5) one of the aphids, Aphis œnotheræ.
A brief account of a chromatin element resembling the accessorychromosome in Sagitta has been added for comparison. Thespermatogenesis of each form will be described in detail, and a generaldiscussion of the results and their relation to the accessory chromosomeand sex determination will follow. The spermatogenesis of the aphid hasbeen included in another paper, but a summary of results and a fewfigures 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'salcoholic sublimate acetic, and corrosive acetic. Flemming's andHermann's fluids followed by safranin gave good results in most cases.The mercuro-nitric solution and Lenhossek's fluid gave excellentfixation and were preferable to the osmic mixtures when it was desirableto stain the same material with iron-hæmatoxylin, and also with variousanilin stains.
Heidenhain's iron-hæmatoxylin, either alone or with orange G orerythrosin, was used more than any other one stain. With osmic fixationsafranin gave better results in some cases, because of the[Pg 4] abundance ofspindle fibers and sphere substance which were stained by hæmatoxylin.The safranin-gentian combination used by Miss Wallace and others in thestudy of the accessory chromosome did not prove to be especially helpfulwith these forms. Thionin was found to be a very useful stain fordistinguishing between the accessory chromosome and an ordinarynucleolus. Licht-grün was often used in combination with safranin.
RESULTS OF INVESTIGATIONS.
Termopsis angusticollis.
In the termite it was not found to be practicable to dissect out thetestes. The tip of the abdomen was therefore fixed and sectioned, youngmales whose wings were just apparent being used. The cells are allsmall, and could not be studied to advantage with less than 1500magnification (Zeiss oil immersion 2 mm., oc. 12).
In the spermatogonium there is a very large nucleolus (plate I, fig. 1),which in the iron-hæmatoxylin preparations is very conspicuous, but doesnot