70 ORIGIN OF SOCIETY. CANTO 11. 



" Now vows connubial chain the plighted pair, 

 And join paternal with maternal care; 

 The married birds with nice selection cull 

 Soft thistle-down, gray moss, and scattered wool, 

 Line the secluded nest with feathery rings, 

 Meet with fond bills, and woo with fluttering wings. 

 Week after week, regardless of her food, 

 The incumbent Linnet warms her future brood; 

 Each spotted egg with ivory lips she turns, 

 Day after day with fond expectance burns, 350 



Hears the young prisoner chirping in his cell, 

 And breaks in hemispheres the obdurate shell. 



The incumbent Linnet, 1. 348. The affection of the unexperienced 

 and untaught bird to its egg, which induces it to sit days and weeks 

 upon it to warm the enclosed embryon, is a matter of great difficulty 

 to explain ; See Additional Note IX. on Storge. Concerning the 

 fabrication of their nests, see Zoonomia, Sect. XVI. 13. on instinct. 



Hears the young prisoner, 1. 351. The air-vessel at the broad end 

 of an incubated egg gradually extends its edges along the sides of the 

 shell, as jthe chick enlarges, but is at the same time applied closer to 

 the internal surface of the shell ; when the time of hatching approaches 

 the chick is liable to break this air-bag with its beak, and thence 

 begin to breathe and to chirp; at this time the edges of the enlarged 

 air-bag extend so as to cover internally one hemisphere of the egg ; 



