52 Sterile and Hybrid Pheasants 



hypertrophied. Assumption of hen's plumage by the cock bird is much 

 rarer and is generally due to hereditary transference of this character 

 independently of any disturbance of the testes or the reproductive 

 function. 



4. The sex-ratio among hybrid pheasants gives a large preponder- 

 ance of males over females (228 j" to 135 %). This preponderance 

 cannot be accounted for by a greater death-rate of female chicks in the 

 shell or subsequently, and must be presumably due to a selective ferti- 

 lisation by which more male zygotes are produced than female, or else 

 to a selective death-rate at so early a stage of developement that no 

 trace of an embryo could be detected. 



EXPLANATION OF PLATE I. 



[All the figures are drawn with the caraera under a 4 eyepiece and ^^.^ objective. 

 Magnification about 1270.] 



Fig. 1. Six spermatozoa of normal common pheasant. (P. torquatus.) 



Fig. 2. Specimens of spermatozoa of hybrid Eeeve's ? by versicolor c? . They show 



abnormality of size, and deformity of shape in some cases. 

 Fig. 3. Section of testis tubule of hybrid Eeeve's ? by versicolor (? . Spg. spermatogonia. 



Spc. 1, primary spermatocytes showing abnormal spireme stage. Sp. secondary 



spermatocytes, spermatids and spermatozoa all showing a high degree of abnormality 



and degeneration. 

 Fig. 4. Section through an outer part of degenerate ovary of hybrid Eeeve's ? by Formo- 



san s (hybrid B). Ep. external epithelium, i. a group of interstitial cells. 

 Fig. 5, Section through an inner part of degenerate ovary of B. i. group of interstitial 



cells. /. fibrous tissue, cy. a cyst. 



LIST OF LITERATURE. 



1. Heinrich Poll. " Mischlingstudien, vl" Archiv f. Mikroskopische Anatomie, 



Bd. 78, 1911. 



2. GuYER, M. F. " On the Sex of Hybrid Birds," Biological Bulletin, Vol. xvi. 



1909, p. 193. 



3. Smith, G. " Studies in the Experimental Analysis of Sex. Part 9. Ou 



Spermatogenesis and the Formation of Giant Spermatozoa in Hybrid Pigeous." 

 q. J. M. S. Vol. Lvin. 1912. 



4. Guthrie, C. G. Journal of Experimental Medicine, Vol. xii. p. 269, 1910. 



5. GooDALE, H. Biological Bulletin, Vol. xx. 1910. 



6. Brandt, A. Zeitschrift /. Wiss. Zool. Vol. xlviii. p. 101, 1889 



