STUDIES ON THE PHYSIOLOGY OF REPRODUCTION 



IN THE DOMESTIC FOWL. 



XVI. DOUBLE EGGS. 1 



MAYNIE R. CURTIS. 



Among the eggs of the domestic fowl an egg which contains 

 another egg is quite rare, but one or more such specimens have 

 been observed by most persons who have handled large numbers 

 of eggs. This phenomenon has excited the interest of poultry- 

 men and scientists and a number of specimens have been de- 

 scribed in the agricultural and scientific literature. The purpose 

 of the present paper is to describe several specimens observed 

 at the Maine Agricultural Experiment Station which have been 

 laid or have been found partly formed within the oviduct at 

 autopsy and to discuss the formation of these abnormalities 

 from the physiological point of view. 



Parker (12) published an extensive bibliography on the 

 subject and discussed at some length the recorded cases in 

 connection with four cases which he had himself observed. 

 Von Durski (6) also cites a number of other cases collected from 

 the literature and gives a bibliography. Summarizing these 

 cases briefly we arrive at the following conclusions: 



1 . Either a normal egg or a dwarf egg which contains little or 

 no yolk may be enclosed with a normal yolk in a second set of 

 normal egg envelopes. The included egg may lie near the 

 yolk of the including egg or it may be enclosed only in the outer 

 layers of albumen. 



2. Either a normal or a dwarf egg may be enclosed in a set of 

 normal egg envelopes without any yolk being present in the 

 enclosing egg. 



3. When the included egg has a blunt and a pointed end 

 which are distinguishable, it always lies with its pointed end 

 toward the pointed end of the including egg. 



1 Papers from the Biological Laboratory of the Maine Agricultural Experiment 

 Station No. 97. 



181 



