Sept. 18. 1916 Dwarf Eggs J 033 



It is seen from Table XXX that 64.96 per cent of all the dwarf eggs 

 produced were apparently initiated by the presence of yolk in the duct. 



The presence of almost normal chalazae in a few of the eggs without 

 yolk suggests that a yolk may sometimes enter the duct, stimulate 

 secretion of chalazae, and then be extruded, leaving behind enough 

 chalazae and albumen to furnish the necessary stimulation for the com- 

 pletion of the egg. 



X.— RELATION OF DWARF-EGG PRODUCTION TO OTHER OBSERVED 

 PHENOMENA OF EGG PRODUCTION WHICH OCCUR IN NATURE OR 

 HAVE BEEN EXPERIMENTALLY PRODUCED AND THE CONTRIBU- 

 TION OF THIS STUDY TO OUR KNOWLEDGE OF THE NORMAL PHYSI- 

 OLOGY OF EGG PRODUCTION 



It has already been noted that five of the six birds on which autopsies 

 had been performed while an egg was in the oviduct or immediately after 

 one was laid were absorbing yolk through the visceral peritoneum. In 

 three cases the dwarf egg also contained yolk. In two of the other cases, 

 however, no yolk was found in the dwarf egg, although the body cavity 

 contained yolk. This suggested, first, that ovulation or a specific condi- 

 tion of the sex organs immediately accompanying it was the essential 

 stimulus for the secretion of the egg envelopes by the duct; or, second, 

 that such a specific condition being present, the secretion of the egg 

 envelopes was stimulated by the small lump of hardened albumen, which 

 in these cases seemed to be the nucleus of the dwarf egg; or, third, that 

 a yolk had entered and then been expelled from the duct. 



That neither ovulation nor any condition of the sex organs associated 

 with it is alone sufficient to cause the formation of a dwarf egg is certain. 

 Birds known to have ovulated into the body cavity for a long time, due 

 either to a morphological, physiological (6), or surgical (16) disturbance, 

 which prevented the yolk from entering the duct but did not otherwise 

 disturb the mechanism, did not produce dwarf eggs. Some stimulus 

 other than the condition of the sex organs is necessary to start the 

 secreting activity of the duct. In normal eggs and in dwarf eggs with 

 yolk this stimulus (mechanical or chemical) is furnished by the yolk. 



The fact that all dwarf eggs without yolks contain some nucleus firmer 

 than normal albumen, together with the fact that in one case where the 

 bird had a dwarf egg with such a nucleus in the shell gland at autopsy no 

 yolk was found in the body cavity, suggests that when the sex organs are 

 maturing and ovulating successive yolks from the ovary a mechanical 

 stimulus may initiate the secretion of the egg envelopes. 



Experiments performed by Tarchanoff (24) and Weidenfeld (27) have 

 shown that a complete set of egg envelopes may be formed around an 

 artificial yolk. Tarchanoff used an amber bead and Weidenfeld used an 

 artificial yolk of wood or rubber. The authors, using a glass marble or 

 an artificial yolk of agar, have confirmed this result. The experiments 



