256 MICHAEL F. GUYER. 



EXPLANATION OF PLATES. 



PLATE I. 



From photographs by the author. Enlargement 1,250 diameters unless other- 

 wise specified. Photos i to 7 are from sections; the remainder, from smears. 



FIG. i. Polar view, metaphase of primordial germ cell in testis of thirteen- 

 day chick; focused to show two characteristic curved chromosomes (one at the 

 right and the other above and to the left); the other chromosomes, mostly out of 

 focus, are rod-like. 



FIG. 2. Tangential view, metaphase of primordial germ-cell in testis of thir- 

 teen-day chick focused to show two characteristic, curved chromosomes; the 

 other chromosomes were out of focus. 



FIG. 3. Showing the two curved chromosomes in a spermatogonium of an 

 adult Rhode Island Red fowl. 



FIG. 4. Showing a single curved element (to the right) in an early germ-cell 

 in the ovary of a ten-day chick. The other chromosomes are out of focus but 

 careful examination showed no other curved ones among them. 



FIG. 5. Polar view, metaphase in nephridial tubule of a ten-day female chick. 

 The single curved chromosome lies well to one side (above) the other chromosomes. 



FIG. 6. Side view of an equatorial plate stage in an ovarian cell of a ten-day 

 chick. A less deeply staining, curved element was attached to one edge (left) of 

 the plate. The photograph does not reveal the curved condition which was readily 

 visible under the microscope. 



FIG. 7. Another ovarian cell in a ten-day chick; condition practically the 

 same as in 6. 



FIG. 8. Side view of a metaphase in a primary spermatocyte of a Plymouth 

 Rock fowl showing the special curved element well toward one pole. X 1,300. 



FIG. 9. Side view of a metaphase in a primary spermatocyte of a Langshan 

 fowl, showing the curved element near one pole. 



FIG. 10. Tangential view of a metaphase in a Rhode Island Red fowl showing 

 the curved element near one pole of the spindle. 



FIG. ii. Side view of a metaphase in primary spermatocyte of a Plymouth 

 Rock fowl showing the curved chromosome. 



FIG. 12. Ditto. The special chromosome is curved toward the observer. 

 X 1,200. 



FIG. 13. Ditto. The special chromosome is curved away from the observer 

 and hence foreshortened in the photo. 



FIG. 14. Side view, metaphase in primary spermatocyte of Langshan fowl, 

 the curved element seen tangentially. 



FIG. 15. Ditto in Plymouth Rock fowl. 



FIG. 16. Showing nature of the spindle in primary spermatocytes (Plymouth 

 Rock). The special element is not visible though probably in the equatorial plate 

 in some such condition as in Photo 32 (polar view). X 1,200. 



FIG. 17. Side view, metaphase in primary spermatocyte of Langshan fowl. 

 The fuzzy appearance of the curved chromosome in this and various other photos 

 is due to a coating of linin-like material which, though in sufficient contrast to the 

 chromosome as seen under the microscope, photographs dark. X 1,300. 



FIG. 1 8. Primary spermatocyte of Plymouth Rock fowl; the special chromo- 

 some curved away from the observer (see Fig. 24 for a different view of a some- 

 what similar stage). 



