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Studies in Spermatogenesis Part II   By: (1861-1912)

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First Page:

STUDIES IN SPERMATOGENESIS

PART II.

(PAGES 33 74. PLATES VIII XV.)

A COMPARATIVE STUDY OF THE HETEROCHROMOSOMES IN CERTAIN SPECIES OF COLEOPTERA, HEMIPTERA AND LEPIDOPTERA, WITH ESPECIAL REFERENCE TO

SEX DETERMINATION.

BY N. M. STEVENS

[Illustration]

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 OF COLEOPTERA, HEMIPTERA, AND LEPIDOPTERA, WITH ESPECIAL REFERENCE TO SEX DETERMINATION.

By N. M. STEVENS.

INTRODUCTION.

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.

METHODS.

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.

COLEOPTERA.

Trirhabda virgata (Family Chrysomelidæ).

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.

In Trirhabda virgata , the metaphase of a spermatogonial mitosis (plate VIII, fig. 3) contains 28 chromosomes, one of which, as in Tenebrio molitor is very much smaller than any of the others. The maternal homologue of the small chromosome is, as later stages show, one of the largest chromosomes. In Tenebrio the unequal pair could not be distinguished in the growth stages of the spermatocytes. In Trirhabda it has not been detected in the synizesis stage (fig. 4), but in the later growth stages (figs. 5 7) this pair is conspicuous in preparations stained by the various methods cited above, while the spireme is pale and inconspicuous. The size of the heterochromosome pair varies considerably at different times in the growth period, and in some nuclei (fig. 7) both chromosomes appear to be attached to a plasmosome. The ordinary chromosomes assume the form of rings and crosses in the prophase of the first maturation mitosis (fig. 8), but usually appear in the spindle as dumb bells or occasionally as tetrads (fig. 10), or crosses (fig. 11). The unsymmetrical pair is plainly seen in figures 9 and 11, but is not distinguishable in a polar view of the metaphase (fig. 13). In the anaphase (figs. 14 16) the larger and the smaller components of the pair separate as in Tenebrio ... Continue reading book >>




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