BIRDS' EGGS 251 



Dwarf Eggs. — It is not very uncommon for a hen to 

 produce dwarf eggs, sometimes spheroidal, occasionally 

 cylindrical. They have been studied by Raymond Pearl 

 and Maynie R. Curtis (1916), who find that 35 per cent, are 

 yolkless. In those which contained yolk, 9 per cent, had no 

 enclosing membrane. The production of a dwarf egg is 

 usually an isolated phenomenon, occurring during the height 

 of the breeding season, and not implying that there is much 

 wrong. In eleven out of two hundred cases, however, no 

 normal eggs were produced after the dwarf egg, and examina- 

 tion showed, in five of these, some pathological condition 

 of the oviduct which interfered with the passage of the egg. 

 A dwarf egg means in most cases that the egg has not 

 received its proper equipment of yolk, perhaps through being 

 liberated from the ovary prematurely. In most of the other 

 cases it means that a shell has formed in the oviduct around 

 a blob of albumen. 



Double-Yolked Eggs. — ^When two ova are liberated from 

 the ovary within an unusually short interval of one another, 

 they are apt to unite in the oviduct. According to the level 

 in the oviduct at which they come together, different types 

 arise. These have been studied in the fowl by Maynie R. 

 Curtis (191 5), who distinguishes three types, connected by 

 gradations. In one type (1603 per cent.) the two yolks 

 (or ova) share the same ensheathments within the shell ; in a 

 second type (70-99 per cent.) the layers that form the 

 chalazae are separate for the two, but all or part of the thick 

 white of egg is common to the two ; in a third type (i2"98 

 per cent.) the two yolks have entirely separate thick albumen 

 envelopes, but are within a common shell-membrane. It is 

 noted that the occurrence of double-yolked eggs may 

 indicate a heightened fecundity, but it may also indicate a 

 low physiological tone in the oviduct. 



Triple-yolked eggs are very rare. Maynie R. Curtis 

 (1914) notes that in the course of six years only three 

 triple-yolked eggs were obtained from more than three 

 thousand fowls. Each was the first egg of a young pullet, 

 as is often the case with double-yolked eggs. An egg 



