140 



SKXIAL MMOhTIIISM 



and more pliant instrument It appears, therefore, that the 

 male and female co-operate in obtaining their food, and it is 

 not improbable that the male makes openings into cavities 

 which the female explores. In this case the dimorphism is 

 not related to courtship and reproduction in the usual way, 

 but is adapted to a special division of labour between male 

 and female in constant companionship. In each sex the 

 special mode of employing the bill is evidently the cause of 

 its special shape and structure ; the mechanical effects on the 



Fig. 14. The Huia of New Zealand. A, male ; B, female. 

 Dictionary of Birds. 



From Newton and Gadow, 



bills would obviously be, in the individuals, in the direction 

 of the modifications actually existing in the species, and it is 

 reasonable to conclude that the individual effects have been 

 accumulated in the evolution. 



Cotingidce. The Cotingidae are a family of Passerine birds 

 belonging to South America, which are sexually dimorphic. In 

 some species of Pipra the secondary wing feathers of the male 

 are much modified, while in the female they are normal. The 

 modification consists in the great thickening of the shaft and 

 the narrowness and distorted shape of the vane. The males 

 make an extraordinary noise by means of these feathers in 



