300 TROPICAL WILD LIFE IN BRITISH GUIANA 



examination of other specimens. That it is of regular occur- 

 rence in the young chicks is assured by the fact that its pres- 

 ence was noted in several hirds at different stages of growth. 



A FEW POINTS CONCERNING THE EMBRYONIC HEAD 



The embryonic bill is short, with a blunt end, somewhat 

 compressed, and both mandibles are of the same length. 

 There is a small "egg-tooth" on the tip of the upper mandi- 

 ble. An examination of several specimens for the length of 

 bill as compared with the adult shows a steady uniformity 

 in the growth of that organ as compared with the age of the 

 chick. 



The nostrils do not appear through the thick membrane 

 of the nasal fossa until near hatching time. In the three-day 

 chick they are small round apertures, 7 mm. from the tip 

 of the bill. As the bird grows older, they gradually increase 

 in length, becoming oval, until in the adult they are twice 

 as long as broad and lie parallel to the culmen. 



The skin flap about the bill extends far up between the 

 great eyes of the embryo, and fills the entire space between 

 them. It consists of a long, soft, loose flap of tissue attached 

 to the base of the bill. In the hatched chicks it hardens and 

 becomes much shorter, taking on the shape and proportion- 

 ate size of the adult wattle. 



TOES AND CLAWS 



The extraordinary length of the claws is of special in- 

 terest in this bird. The claw of the hind toe greatly length- 

 ens as the bird matures until it far surpasses any of the oth- 

 ers. In the embryo it is very little longer than the rest and 

 composes about one-third of the toe. The other claws are 

 of normal size, blunt at the end and extend straight out from 

 the toe with a slight downward curve. 



After the jacana is hatched the hind claw commences 

 to grow rapidly while the others remain stationary, except 



