6 CONTENTS. 



Faqb. 



14. Skeletal dimensions 63 



The data on skeletal dimensions 63 



Comparison of skeletal dimensions 65 



The average dimensions 65 



Coefficients of variability of dimensions 69 



15. The skull sutures 72 



16. Miscellaneous morphological characters 74 



The interparietal bone 74 



The shape of the skulls 74 



The effect of sterility in the males 75 



Anomalies occurring in the hybrids 76 



17. General conclusions as to growth and morphological characters 77 



Part III. The Febtilitt of the Pabent Species and Htbbtds. 



18. Introductory discussion 79 



19. The fertility of the male hybrids 85 



Materials and methods 85 



The results of the simple breeding tests alone 87 



The results of all microscopic tests 88 



The results of a combined microscopic and breeding test 90 



The inheritance of sterility 92 



The male offspring of fertile male hybrids 97 



The secondary sexual characters 99 



20. The fecundity of the female hybrids 100 



21. The sex ratio in the hybrids 101 



22. Summary and general conclusions 103 



Tables 104 



BiBLIOGBAPHY 129 



Descbiption of Plates 133 



