DEVELOPEMENT OF BIRDS. 265 



sixth.' ^ As the contents of the egg become condensed by em- 

 bryonal developement, the air-cavity, fig. 130,/, expands. ^ The 

 chick some time before birth has a kind of mixed action of life, 

 for it breathes, and we can hear it pip and chirp in the egg ; and 

 Ave find the adult circulation throuo-h and out of the heart is 

 formed before birth : yet it is receiving its nourishment from the 

 remaining slime.' ^ 



The ' slime ' or albumen is reduced to the small mass adhering 

 to the cicatrix of the vitellicle, and with this and its yolk little 

 decreased in bulk, it is taken into the abdomen, Avhere it serves to 

 nourish the chick in the first feeble days of its free life : the pedicle 

 of the vitellicle communicates with a loop of the small intestine. 

 The allantois is left, lining the shell : the urachus is obliterated. 

 The anus has a dorsal position near the hind end of the trunk in 

 the nestlings, fig. 113, A. 



The degree of developement under wliich the young bird quits 

 the egg differs in different groups of the class. It is naked ^r 

 covered with down only, and is dependent on the parents for 

 shelter and support, in the orders Raptoees, Scansores, Yoli- 

 TORES, Cantores, in the Rasorial suborder Gemitores (Doves, 

 p. 9) ; in the Grallatorial Cidtrirostres (Herons, &c. p. 9) ; in the 

 Natatorial LongijiennatcB (Gulls, &c. p. 9), and TotijialmatcR 

 (Pelicans, &c. p. 9). The young bird is excluded well clothed 

 and able to run or swim about and provide food for itself in the 

 suborder Gallinace^, in the Cursores, in the Natatorial 

 BrevipennatcB (Penguins, Awks, &c.) and Lamellirostres (Duck, 

 Goose, &c.), and in all the Grallatores save the Cultrirostral 

 group or part of it. Of these ' precocious ' birds {Prcecocesymo&t 

 are polygamous, and the females hatch many young ; whereas in 

 the * nursing ' groups {Altrices) the species are monogamous, and 

 have few young. ^ 



' Three of the figures here referred to by Hunter arc engraved in xx. vol. v. pi. 

 Ixxvi. figs. 16, 17, 18. 2 iij, p, xxvii. ^ vir. p. 265. 



