156 SEXUAL DIMORPHISM 



anything in the external influences, such as light or food, 

 which could affect the sexes differently. 



In the Charadriidse, or intermediate between rails and 

 snipes, are three species of the genus Rhynchcea in which 

 the females are not only larger, but much more richly 

 coloured than the males. 1 In Rhynchcea australis the 

 trachea is simple in the male, while in the female it makes 

 four distinct convolutions before entering the lungs. The 

 male undertakes the duties of incubation. The female 

 doubtless uses her voice in calling to the male, and the 

 pressure of the air has caused the convolutions of the trachea. 



Psittaciclce. Sexual differences in colour occur in 

 certain parrots. One of the most striking cases is that of 

 Edectns polychloros, of which the males and females were 

 originally described as distinct species. Well -mounted 

 specimens of these birds are to be seen in the Hunterian 

 Museum of the College of Surgeons in London. The male 

 is green, the female brilliant red and blue. Mr. Beddard 2 

 states that there is no difference in the pigments present 

 in the two sexes in this species. In birds many colours, 

 especially those known as metallic or iridescent colours, are 

 due to minute structural markings on the feathers. They 

 are produced by the phenomenon known in optics as the 

 interference of the reflected rays of light. The case of 

 Eclectus thus appears to be analogous to that of the Dragonet 

 and other fishes, where also the same elements of coloration 

 are present, but quantitative differences in these in the two 

 sexes produce markedly different colours. I am unable 

 at present to attribute the difference in colour between the 

 sexes in Eclectus to any difference in the habits or conditions, 

 of life, but it is not improbable that proper investigation 



1 Jerdon's Birds of India, vol. iii. Gould's Handbook to tlie Birds of 

 Australia. 



2 Animal Coloration, p. 4. London : Swan, Sonnenschein and Co., 1892. 



