SIZE, SHAPE AND PHYSICAL CONSTITUTION OF THE EGG. 13I 



upon the deposition of yolk. The teleological view that the 

 oviduct enlarges in order to be ready to lay the first egg is not 

 tenable. Normally the oviduct enlarges while the yolks enlarge 

 and reaches functional efficiency by the time the first yolk Is 

 mature. 



The stimuli which initiate the peristaltic action of the oviduct 

 and attract the funnel to the mature folicle are among the un- 

 solved problems of physiology. The yolk is already oriented 

 in the follicle before the funnel encloses it. In pigeons * both 

 chalazal and polar axes are determined in the primordial folli- 

 cle ; the first by the long axis of the oocyte and the second by 

 the eccentric germinal vesicle. The polar orientation of the 

 Qgg in the follicle is due to the action of gravity after the yolk 

 becomes movable in the follicle (at the time of the formation 

 of the zona radiata). The vegetative pole is heavier than the 

 animal pole, hence the animal pole comes to lie beneath the 

 stalk of the follicle. 



Due to the pressure of the inclosing funnel and to increased 

 internal pressure, the yolk ruptures the follicle and becomes 

 free in the duct. At this time the secreting activity of the duct 

 begins. Again the precise nature of the stimulus is not cer- 

 tainly known. It is normally connected with the presence of 

 the yolk; but albumen secretion followed by normal membrane 

 and shell formation have been induced in functioning oviducts 

 by the insertion of artificial yolks. Results of this kind are 

 reported by Weidenfeld t and Tarchanofif.* Unpublished inves- 

 tigations at this laboratory have also shown that an egg may be 

 formed around an artificial yolk or the artificial yolk may be 

 fastened in the upper part of the oviduct and an egg may be 

 formed which contains chalazae, both kinds of albumen, normal 

 membrane and shell. This last result as well as the not infr^ 

 quent occurrence of small yolkless eggs which contain all the 

 other normal egg parts show that the secretory process may 



* Bartelmez, G. W. Loc. cit. 



t Weidenfeld. Verb, der Ornithol. Gesellschaft, Bayern, 1905, p. 

 112. 



X Tarchanoff, J. R. Ueber die Verschiedenbeiten des Eiereiweisses bei 

 befierdert geborenen (Nestfluchter) und bei nackt geborenen (Nes- 

 thocker) Vogeln und iiber die Verhaltnisse zwischen dem Dotter und 

 dem Eiereiweiss. Pfliiger Archiv fiir Physiologie, Vol. 32, 1884. 



