GENERAL CHARACTERS Of BIRDS. 



653 



The (metanephric) kidneys art three-lotted^ and lie embedded 

 in the pelvis ; the ureters open into the cloaca ; there is no 

 bladder / the urine is semi-solid, and consists chiefly of urates. 

 Water must be mainly got rid of by evaporation from the 

 walls of the air-sacs and air-passages. 



The testes lie beside the kidneys ; the vasa deferentia run 



FIG. 358. Young bearded griffin (Gypaetus barbatus], After Nitzsch. 



Showing the feather-tracts or pterylae, for instance those on the breast 

 (JPT.). ., ear; />., web or propatagium ; 77/., thumb; PR., bases 

 of primary feathers ; S., bases of secondary feathers ; B.S., bare streak 

 without pterylae ; CL., cloaca ; R. t bases of rectrices or tail feathers, 



outside the ureters, and open into the middle region of the 

 cloaca. The right ovary atrophies, the right oviduct is rudi- 

 mentary. There is rarely any copulatory organ, but it is 

 large in ostriches, ducks, geese, and some other birds. 



The eggs have much yolk and hard calcareous shells. The 

 segmentation is meroblastic and discoidal. The allantois is 

 chiefly respiratory, though it helps in absorbing the nutritive 



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