6 SEX AND HEREDITY 



out against the inner surface of the shell, gradually lining 

 the whole of it and serving as the breathing organ by 

 which the young bird absorbs the oxygen necessary to 

 its life, through the pores of the shell. The remains of 

 the allantois may be seen as a thin membrane containing 



to 



' r , 



uc. 



FIG. 45. 



Young fowl extracted from an egg which has been incubated for 4^ days. 

 all, allantois ; C.H, cerebral hemispheres of brain ; E, eye ; som, edge of opening 

 through which the allantois and yolk-sac project ; t.o, optic lobes of brain ; V, 

 heart ; v.c, gill-openings ; y.s, yolk-sac. (From Graham Kerr's Embryology.} 



a rich network of bloodvessels lining the pieces of shell 

 from which a young bird has hatched. 



The Mammals those animals which possess hair and 

 feed their young on milk constitute the group to which 

 we ourselves belong, and so we speak and write of them 

 as the highest of living things just as no doubt an Ant 

 or a Cuttlefish, were it able to write books, would place 

 in this position the Insects or the Molluscs ! 



