J. E. DUERDEN 



153 



Bald Head Patch. 



The bald head is another character involving an ontogenetic loss 

 of plumes of somewhat the same nature as that connected with the leg 

 (Fig. 5). In this case however the loss affects only the North Afi-ican 

 ostrich and not the South African, and represents an accepted specific 

 feature, whereas the disappearance of the leg contours occurs through- 

 out the race. At the time of hatching the head of all ostrich chicks 

 is covered, except over the pineal patch, with short bristly down, which 

 later on is replaced by longer down with hair-like prolongations of the 

 barbs. In the southern bird this covering persists, a still longer tuft 



Fig. 5. Bald head patch of Northern ostrich. The clear oval area behind represents the 



pineal spot. 



of bristly feathers often forming on the crown of the head. In the 

 northern, on the other hand, the feathers begin to fall out when the 

 chick is about three months old, and by six months an oval, bald patch 

 is formed, varying somewhat in extent in different birds, and repre- 

 senting a definite mutation. The skin also becomes scurfy and the pits 

 of the feather follicles disappear. In crosses with the southern bird 



