200 MAYNIE R. CURTIS. 



of a normal egg does not exhaust even temporarily the oviduct 

 glands since both albumen and shell are heavier in double- 

 yolked than in single-yolked eggs, while both parts are still heavier 

 in triple-yolked than in double-yolked eggs. It was further 

 shown (3) that in many cases the second yolk must have followed 

 the first quite closely since a normal egg was produced on the 

 day preceding the day on which the multiple-yolked egg was 

 laid. The time between the passage of these yolks must have 

 been less than the time required to form a complete hard shell. 

 The very plausible explanation offered by Hargitt does not, 

 therefore, seem tenable. Two other suggestions may be made 

 but neither of them can be proven at present. One is that 

 perhaps the oviduct is polarized to such an extent that secre- 

 tion is discharged only when the stimulus advances in the normal 

 direction. The other is that perhaps the egg moves very rapidly 

 up the duct and that there is not sufficient time for the stimulus 

 to become effective. That the egg does move rapidly up the 

 duct is suggested by the fact that in the birds with ducts ligated 

 in the shell gland the eggs with complete shells are forced up 

 the ducts before the succeeding yolks enter the funnels. Nor- 

 mally ovulation takes place very soon after laying. 



It should, however, be stated that there are a few cases known 

 where some portion of the duct has for some reason failed to 

 form its normal secretion around an egg which has passed in the 

 normal direction. The two cases which have come under our 

 personal observation may be briefly cited. A photograph of 

 the egg produced in the first case is shown in Plate III., Fig. 3. 

 When the egg was found in the nest the two parts were pressed 

 together over the dark areas which face each other in the photo- 

 graph. They were held together only by the thin layer of 

 shell which covers all of the two egg membranes except the 

 approximated portions. This shell cracked off when the egg 

 was handled and the circular areas free from shell were exposed. 

 The two eggs had apparently been flattened together but the 

 membrane rounded up as they separated. The egg shown at 

 the right was a normal egg with normal yolk, albumen and egg 

 membrane. The other egg was a normal yolk surrounded by an 

 egg membrane. This egg contained no visible albumen. When 



