sept. 18, 1916 Dwarf Eggs 1037 



apparently precedes ovulation. Further work is necessary, however, to 

 determine the factors involved in the specific condition of the duct which 

 causes it to respond to stimulation by the secretion of the egg envelopes. 



It would seem from the above considerations that the presence in a 

 completely functional oviduct of a small solid or semisolid substance 

 capable of presenting a mechanical stimulation may cause the production 

 of a dwarf egg. Nearly two-thirds of the dwarf eggs, however, are known 

 to be initiated either by abnormally small yolks or by parts of broken 

 yolks. Their production may be associated with an abnormal condition 

 of the ovary or with pathological conditions of the duct, but even in 

 these cases the result was due not to the abnormality per se but to the 

 fact that this abnormality prevented the entrance of a normal yolk or 

 obstructed its passage through the duct. 



The mechanical stimulus need not begin at the funnel in order to be 

 effective to the parts of the duct lower down. In Tarchanoff's case (24) 

 and in one of our own cases of perfect egg formation around an artificial 

 yolk, the yolk was inserted into the duct through a slit in the albumen 

 portion, the duct being tied off above this point. Pearl and Surface (18) 

 showed that a mechanical stimulation (in this case feces introduced by 

 anastomosing the intestine to the side of the uterus) caused the formation 

 of shell by the uterus. 



The mechanical stimulation is of local character — that is, it is not 

 transmitted down the duct for any measurable distance below the point 

 where it is applied. Pearl and Curtis (16) have shown that "the stimu- 

 lation of the advancing egg is necessary for the discharge of the secretion 

 of the duct, since a duct closed at any level functions only to the point 

 where the passage is interrupted." In the cases of dwarf -egg pro- 

 ducers with pathological ducts the abnormality of the duct was in each 

 case of a nature to constrict but not close the lumen of the duct. Sev- 

 eral eggs produced by these birds contained lumps of yolk, indicating 

 that the nucleus of the egg had passed the constricted portion. 



SUMxMARY 



(1) During the eight years from February 1, 1908, to February 1, 

 1 91 6, 298 dwarf eggs are known to have been produced at the poultry 

 plant of the Maine Experiment Station. 



(2) During the two years of maximum dwarf-egg production the 

 ratio of dwarf eggs to normal eggs was 1 dwarf egg to 1,158 normal 

 eggs. 



(3) Dwarf eggs are of two distinct types in respect to shape: First, 

 the prolate-spheroidal type, and second, the cylindrical type. 



(4) Dwarf eggs of the prolate-spheroidal type are much more fre- 

 quently produced than the cylindrical type. In fact 95.4 per cent of 

 the dwarf eggs studied were prolate spheroids. 



