396 RAYMOND PEARL AND M. R. CURTIS 



are not yet fully understood. Pearl and Surface ('09 a) published 

 a short report of a preliminary investigation of the stimulus 

 which sets up the shell secreting activity. They showed that 

 when the intestine was anastomosed to the oviduct above the 

 uterus the faeces extruded through the vagina or retained in 

 the uterus were covered with a deposit of shell material. They 

 concluded that the immediate effective stimulus to shell secre- 

 tion is mechanical and that shell formation is a local reflex 

 not dependent upon a specific activity of other parts of the 

 reproductive apparatus. 



3. The amount of secretion by the duct depends in part 

 upon the intensity of stimulation. Within the eggs of the same 

 individual the weight of albumen is highly correlated with 

 the weight of the yolk and the weight of shell is significantly 

 positively correlated with the weight of both albumen and 

 shell (Curtis '14 a). In yolkless, single, double and triple- 

 yolked eggs the weight of albumen and shell are directly related 

 to the number of yolks contained (Pearl '10, and Curtis '14 b). 



4. The muscular activity of the walls of the oviduct are un- 

 doubtedly responsible for the shape of the egg (Pearl '09, and 

 Curtis '14 b). Further this muscular activity is capable of 

 regulatory changes. Pearl ('09) described the case of a pullet 

 whose first eggs were much longer in proportion to their breadth 

 than any other eggs produced at the Maine Station plant. There 

 was a progressive regulatory change in the eggs of this bird 

 until they finally became normal in shape. 



5. The resection of one-fourth of the albumen secreting 

 region and an end-to-end anastomosis of the remaining parts 

 does not cause a permanent loss of function of the oviduct. 

 Pearl and Surface ('08) described the results of such an opera- 

 tion. The bird began to lay four months after the operation. 

 The eggs were only a little below the average size for the breed 

 and appeared to have a normal proportion of albumen. There 

 seems here also to be a compensatory action of the duct so that 

 the amount of secretion is nearly normal. Whether there is an 

 increase in the number of albumen glands or in the functional 

 activity of those left is not known. 



