344 SAUROPSIDA (birds). 



Fallopian tube in the female ; this single ovary is that of the 

 left side. I have sometimes in the fowl found the right ovary 

 more or less developed. The oviduct is a long tortuous tube in 

 which the ovum receives first the " white " or albuminous cover- 

 ing of the yolk. Towards the end of the egg-tube dilatations 

 appear : in these the eggs receive the shell, which consists of 

 carbonate of lime. A deficiency of this in the bird's system 

 results in so-called " soft eggs." The egg is then passed into 



Fia. 180.— Ovary or Bikd. 



a, c, c, Ova in various stages of development ; 6, streak without vessels indicating 

 the point where the vesinle is about to rupture to allow ova to escape ; d, ruptured 

 vesicle ; e, very small ovrnn showing cicatricula. (Chauveau.) 



the cloaca, and so out of the vent. The eggs of birds are hatched 

 by incubation. The young are provided with a curious calcareous 

 knob on the upper mandible, by means of which they crack a 

 hole in the eggshell when ready to escape. Some can feed as 

 soon as they have escaped from the eggshell^ — precocious young; 

 others have to be fed by the parents — nestlings. 



Birds are found in all climates, and may be residents, 

 migrants, or gipsy-migrants. 



