The Sex-Chromosomes in Ascaris felis. 
313 
1908. Payne, F. On the Sexual Differences of the Chromosome Groups in Galgulus 
oculatus. Biol. Bull. Vol. XIV. 
1905. Stevens, N. M. Studies in Spermatogenesis with Especial Reference to the 
“Accessory Chromosome”. Carnegie Inst. Publ. (36). 
1908. — A Study of the Germ Cells of Certain Diptera, with Reference to the Hetero- 
chromosomes and the Phenomena of Synapsis. Journ. Exp. Zool. Vol. V. 
1910. — The Chromosomes in the Germ Cells of Culex. Ibid. Vol. VIII. 
1911a. — Further Studies on Heterochromosomes in Mosquitoes. Biol. Bull. 
Vol. XX. (2). 
1911b. — Preliminary Note on Heterochromosomes in the Guinea Pig. Ibidem. 
Vol. XX (2) 
1905a Wilson, E. B. Studies on Chromosomes. I. The Behavior of the Idiockromo- 
somes in Hemiptera. Journ. Exp. Zool. Vol. II. (3). 
1905b. — II. The paired Microchromosomes, Idiochromosomes and hetcrotropic Chro- 
mosomes in Hemiptera. Ibid. Vol. II. (4). 
1905c. — The Chromosomes in Relation to the Determination of Sex. Science. N. S. 
Vol. XX. (564). 
1906. — III. The sexual Differences of the Chromosome Groups in Hemiptera, with 
some Considerations on the Determination and Heredity of Sex. Journ. 
Exp. Zool. Vol. III. (1). 
1911a. — The Sex Chromosomes. Arch. f. mikrosk. Anat. Vol. LXXVI. 
1911b. — VII. A Review of the Chromosomes of Nezara; with some more general 
Considerations. Journ. Morph. Vol. XXII. (1). 
Explanation of Plate XXVIII. 
Ascaris felis. 
The figures were drawn with a Zeiss 2 mm. oil immersion objective and a Zeiss 
compensating ocular 12, giving a magnification of 2280. 
Figs. 1 and 2. Nuclei of first spermatocytes with eight bivalent autosomes and 
the XY-pair of idiochromosomes. 
Fig. 3. Equatorial plate of first division, polar view. 
Fig. 4. Equatorial plate of first division, side view, optical section. Only three 
of the eight autosomes are drawn. 
Fig. 5. Optical section of the first division metaphase. 
Fig. 6. First division anaphase, side view. 
Fig. 7. First division late anaphase: daughter groups of eight autosomes, the 
lower having in addition the X-chromosome, the upper, the Y-chromosome. 
Fig. 8. Chromatin group of second spermatocyte : eight autosomes and the 
X-chromosome. 
Figs. 9a und b. Second division. Optical sections of equatorial plates of two 
sister-spermatocytes. The lower shows the X-chromosome, the upper the Y-chromosome. 
