GROWTH AND DEVELOPMENT 



79 



demarkation between one and the other since the moult is in constant progress until the bird 

 reaches maturity. Even while the chick is in its natal down* the flight feathers or remiges 

 are developing. In like manner when the juvenile plumage covers most of the body, the na- 

 tal down is still present in certain feather tracts while the mature plumage is developing in 

 others. In certain instances the natal down is replaced directly by feathers identical in pat- 

 tern and structure to those of the mature plumage. Thus the intermediate juvenile feather 

 does not occur in this sequence. 



Natal Plumage 



At the time of hatching, the body of the grouse chick is almost completely covered with 

 feathers that are popularly called down.* All of the spaces, i.e., areas between the regular 

 feather tracts, are bare although they are obscured by the fluffy down. The most conspic- 



Doug Finch 



THREE GROUSE CHICKS SIX HOURS AFTER HATCHING 



uous of these are the areas over the lungs (which are directly beneath the folded wings), 

 the web of the wings and also the sides of the abdomen. The down as well as some of the 

 flight feathers begins its development during the early stages of incubation of the egg and 

 growth apparently is uninterrupted by hatching. 



* Tcrhiiiinlly the featluTs ii( tliis* pliimuge are neossMptiles. true il.iHti fi-alhers ( iiluimilae I being ahs.'nt. p. 59. 



