Studies in Spermatogenesis (Part 2 of 2)

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.

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.
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.

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.