252 THE BIOLOGY OF BIRDS 



with three yolks represents the extrenie of rapid egg- 

 production ; it is in line with the production of two eggs 

 united by a membranous tube, or of two eggs simul- 

 taneously, or of two eggs on the same day. The yolks or 

 the yolk-laden ova come together in the oviduct and are 

 enclosed in one shell ; the particular type depends on the 

 position in the oviduct, between the funnel and the isthmus, 

 where the coalescence takes place. 



An interesting correlation exists between an increase in 

 the comb in hens and the incidence of an egg-laying period. 

 Geoffrey Smith showed (191 1) that the increase of the comb 

 in the hen is due to a fatty infiltration of the central con- 

 nective tissue core of the comb, and that decrease is due to 

 the abstraction of fat. The cock's comb contains only 

 comparatively small quantities of fat in the central core, the 

 substance of the comb consisting mainly of fibrous connective 

 tissue. The cock's comb does not exhibit marked fluctua- 

 tions in size as the hen's does. Geoffrey Smith pointed 

 out further that the increase in the hen's comb is not accom- 

 panied by a rise in general body-weight, though such a rise 

 usually occurs some time before the enlargement. The 

 explanation of the fatty infiltration is to be found in the fact 

 that at the egg-laying periods the blood becomes charged 

 with fatty material which is conveyed to the ovary and forms 

 part of the yolk of the ova. The excess of this fatty material 

 is deposited in the comb, and probably in other situations 

 as well. 



A little point of some interest in connection with egg- 

 laying in hens is that the yellow pigmentation about the head 

 and legs seems to decrease in the course of vigorous egg- 

 laying. It is suggested by A. F. Blakeslee and D. E. Warner 

 (191 5) that the laying removes yellow pigment in the yolks 

 more rapidly than it can be replaced by the normal meta- 

 bolism, and that in consequence the ear-lobes, the beak, and 

 the legs become pale by the subtraction of pigment. It is 

 not against this suggested correlation to point out that other 

 conditions apart from egg-laying may bring about a similar 

 paleness. 



