SIZE, SHAPE AND PHYSICAL CONSTITUTION OF THE EGG. 1 3 1 
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 
egg 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 oi 
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reported by Weidenfeld t and TarchanoffU Unpublished inves- 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. Verh. der Ornithol. Gesellschaft, Bayern, 1905, p. 
1 12. 
t Tarchanoff, J. R. Ueber die Verschiedenheiten des Eiereiweisses bei 
befierdert geborenen (Nestfluchter) und bei nackt geborenen (Nes- 
thocker.) Vogeln und fiber die Verhaltnisse zwischen dem Dotter und 
dem Eiereiweiss. Pfliiger Archiv fiir Physiologie, Vol. 33, 1884. 
