BILATERALITY OF THE PIGEON's EGG 293 



down the oviduct first, can therefore be traced back to the pri- 

 mordial foHicle. The chief factor, then, in the orientation of 

 the follicle is the fact that the egg is heavier at one end of the 

 long axis and, in the normal position of the bird, this end gravi- 

 tates toward the cloaca. In some cases the position of the 

 ovarian stalk corresponding to that of the latebra may also help 

 in the orientation, but this not a constant feature. The orien- 

 tation of the follicle in the oviducal axis is due, in the pigeon, 

 primarily to the activity of the funnel; its pressure from without, 

 together with the ever increasing pressure from within, i.e., from 

 the continued yolk secretion, are the main factors in the ruptur- 

 ing of the follicle. 



The pressure due to yolk secretion is considerable as may be 

 judged from the way in which the egg bulges out when the rup- 

 turing of the follicle begins and also fr.om the observation that 

 the egg is over a millimeter in diameter greater after ovulation 

 than the whole follicle was before. 



The funnel can exert considerable pressure, for its wall is mus- 

 cular and it is attached anteriorly by part of the dorsal oviducal 

 ligament to the left body wall and posteriorly by the ventral 

 ligament to the ventral margin of several coils of the oviduct. 

 Miss Curtis ('10) has clearly brought out these latter relations 

 in the hen and made several illuminating suggestions on ovula- 

 tion. She describes a 'pocket' formed by the body wall, the left 

 abdominal air-sac and the intestine with its mesentery on the 

 right side, surrounding the ovary. The mouth of this pocket 

 is occupied by the funnel. These relations undoubtedly play a 

 part in the orientation of the follicle and ovulation, and decrease 

 the possibility of the egg escaping into the body cavity. In the 

 pigeon however, I believe that the peristaltic action of the funnel 

 and the yolk secretion are the principal factors in orientation 

 and ovulation, for all these other conditions may be modified by 

 keeping the bird on her back during ovulation and still the ovum 

 succeeds in entering the oviduct. 



The orientation may take place in the course of two and a half 

 to three hours, which is the time that elapses between the laying 

 of the first egg and the rupture of the second from the ovar}^ 



JOURNAL OF MORPHOLOGY, VOL. 23, NO. 2 



