STUDIES IN SPERMATOGENESIS
PART II.
(Pages 33-74. Plates VIII-XV.)
A COMPARATIVE STUDY OF THE HETEROCHROMOSOMESIN CERTAIN SPECIES OF COLEOPTERA,HEMIPTERA AND LEPIDOPTERA, WITHESPECIAL REFERENCE TO
SEX DETERMINATION.
BY N. M. STEVENS
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.
STUDIES IN SPERMATOGENESIS.—II.
A COMPARATIVE STUDY OF THE HETEROCHROMOSOMES IN CERTAIN SPECIES OFCOLEOPTERA, HEMIPTERA, AND LEPIDOPTERA, WITH ESPECIAL REFERENCE TO SEXDETERMINATION.
By N. M. Stevens.
INTRODUCTION.
In Part I of this series of papers, the spermatogenesis of five speciesbelonging to four different orders of insects was considered. In twospecies of Orthoptera an "accessory chromosome" was found; in Tenebriomolitor, one of the Coleoptera, an unequal pair of chromosomes wasdescribed; in the other species no heterochromosomes were discovered.The apparent bearing of the chromosome conditions in Tenebrio molitoron the problem of sex determination has led to a further investigationof the germ cells of the Coleoptera. One of the Hemiptera homoptera andtwo of the Lepidoptera have also been examined for comparison with theColeoptera and the Hemiptera heteroptera.
METHODS.
As a result of previous experience with similar material, only twogeneral methods of fixing and staining have been employed: (1) Fixationin Flemming's strong solution or Hermann's platino-aceto-osmic, followedby either Heidenhain's iron-hæmatoxylin or Hermann's safranin-gentianstaining method (Arch. f. mikr. Anat. 1889). (2) Fixation after Gilson'smercuro-nitric formula, followed by iron-hæmatoxylin, Delafield'shæmatoxylin and orange G, Auerbach's combination of methyl green andacid fuchsin, or thionin.
The iron-hæmatoxylin with either mode of fixation gives by far the mostsatisfactory preparations for general study. The other stains were usedmainly for the purpose of distinguishing between heterochromosomes andplasmosomes in resting stages of the nucleus.
COLEOPTERA.
Trirhabda virgata (Family Chrysomelidæ).
Two species of Trirhabda were found in larval, pupal, and adult stageon Solidago sempervirens, one at Harpswell, Maine, the other at WoodsHole, Massachusetts. The adult insects of the two species differslightly in size and color, the germ cells mainly in the number ofchromosomes, Trirhabda virgata having 28 and Trirhabda canadense 30in spermatogonia and somatic cells.
In Trirhabda virgata, the metaphase of a spermatogonial mitosis (plateVIII, fig. 3) contains 28 chromosomes, one of which, as in Tenebriomolitor is very much smaller than any of the others. The maternalhomologue of the small chromosome is, as later stages show, one of thelargest chromosomes. In Tenebrio the unequal pair could not bedistinguished in the growth stages of the spermatocytes. In Trirhabdait has not been detected in the synizesis stage (fig. 4), but in thelater growth stages (figs. 5-7) this pair is conspicuous