REPRODUCTIVE CYCLE. 105 



In Chapter VIII the author gave but two proofs of his hypothesis. These 

 were the phylogenetic history of incubation and the fact that the incubation period 

 can be shortened by over-feeding. The conception is further supported by the 

 phenomenon of "pumping"; the cycle is disrupted after the eggs are laid, and the 

 birds are thus kept in a continued state of sexual activity throughout the season. 

 Whitman (Vol. II) and later Riddle have found that this procedure develops 

 germinal weakness, a condition which results in an increase of infertility, a greater 

 percentage of partial embryonic developments, and an excessive proportion of 

 females. The following quotation from Fulton (p. 35) is also apropos : 



"The result is likely to be the ruin of the constitution of the hen; for if she is what is called a free 

 breeder, or lays her eggs fast, before the season is over she becomes so weak as in many cases to 

 become ruptured, and in other cases barren, when she is of course valueless. The cause of this is 

 not only excessive laying indeed a young and rank hen will often lay, like a fowl, whether she be 

 mated or not but the cock-bird continually driving her to nest and teasing her while in her weak 

 state, which causes her weakness of course to increase, until the ovary gives way, and she becomes 

 what is termed "down behind." .... We have known some persons, by what is called 'pumping ' 

 a hen, or breeding from her as long as possible, to obtain 8 or 9 pairs of eggs from her in one season ; 

 but we have seldom known more than half reared, and often some of these would have crooked 

 breast bones, which is a great fault as well as a sign of weakness. And as to the hen herself, she is, 

 as already stated, if not entirely, seriously debilitated for life, so that none of her after progeny will 

 be as vigorous as they ought to be." 



There are certain features as to the division of labor in incubation that deserve 

 comment. The impulse seems to develop rather independently in the two birds, 

 though later there is certainly some degree of interaction. It is suggested that the 

 impulse to sit is continuous in both birds, that each bird is desirous of sitting at 

 all times, and in fact would do so if it were not for the need of food, the necessities 

 of bathing and defecation, the desire for some form of alleviating activity, and the 

 insistence of the mate in participating in these duties. This conception accounts 

 for the fact and mechanism of interchange, and the tendency for each bird to do 

 double duty in case of defection on the part of the mate. The female, because of 

 her more exhausting sexual activities, which involve the forming and laying of 

 eggs, is dominated by the stronger impulse, with the greater need for rest and 

 recuperation, and as a consequence she begins earlier, stops later, and puts in much 

 more time during the day. The early irregularity of incubation, we are told, 

 delays the hatching of the first egg relative to the second, so that both hatch more 

 nearly at the same time than they otherwise would. This result possesses the 

 advantage of securing a greater equality in the feeding of the two young. The 

 delay on the part of the male tends to secure a further advantage in that the male's 

 activity does not interfere with his mate's duties in the matter of the laying of the 

 second egg. In this connection we may note the fact that in Ectopistes, which lays 

 but one egg, both birds start incubation previous to egg-laying. 



NESTING. 



In the nesting activities the existence of an impulse and its development from 

 the previous sexual activities is evident. Nesting occurs only as a part of the 

 sequence of activities, and when the impulse is satisfied the activities cease. The 



