SECONDARY CHARACTERISTICS 15 



reproductive differentiations and combative require- importance 

 ments, but also in the metabolic factors of the physio- 

 logical economy. 



Everyone is familiar with the ornamental feathers of 

 the male Bird of Paradise, with the claspers of the male 

 frog, with the antlers of the stag and with many other 

 morphological sex-differentiations too numerous to 

 enumerate. But behind these morphological variations 

 lie physiological differences in the two sexes which are 

 undoubtedly responsible for the more obvious morpho- 

 logical features. It is known, for instance, that in some 

 caterpillars the blood differs in colour in the two sexes, 

 being green in the females and yellow or colourless in 

 the males 1 . This, of course, indicates that the chemical 

 composition of the blood is different in the two sexes. 

 And differences if less obvious than the example just 

 mentioned may be traced in the higher animals. 

 Bucura 2 , referring to the researches of many observers, Far-reaching 

 points out that the human male uses more oxygen than gJ^daJL 

 the human female, and that in men the blood has a character- 

 higher specific gravity, more red corpuscles and a higher 1S 

 percentage of haemoglobin than in women. And these 

 are only gross distinctions. The finer, and probably 

 more important, have not been fully worked out, but 

 I shall refer later to some of the differences which are 

 dependent on the internal secretions, and are of the 

 highest importance. Some day, perhaps, we shall be 

 able to base our knowledge of these physiological 

 and morphological dissimilarities on the variations 

 to be found both quantitative and qualitative in 

 the primary sex-characteristics of the hormonopoietic 

 organs. 



In the human subject the secondary characteristics 

 of the two sexes, when well-differentiated, appear to be 

 strongly contrasted, as is shown in the following 

 columns : 



1 Geddes, P., and J. A. Thomson. Sex, 1914. 



3 Bucura, C. J., Geschlechtsundterschiede beim Menschen, Wien und 

 Leipzig, 1913, p. 12. 



