° igi2 J Gross, The Ydlow-billed Tropic-bird, 69 



are: longest diameter 5.6 cm., shortest diameter 4.1 cm., weight 40.9 

 grams. 



Fig. 9. Egg pipped and some of the calcareous shell broken away. 

 The shell membrane, however, is intact except where it is pierced by the 

 beak of the embr3'o. The measurements are: longest diameter 5.4 cm., 

 shortest diameter 3.9 cm., weight before being pipped 44 grams. 



Fig. 10. Same egg as shown in fig. 9, but after the shell membrane had 

 been ruptured. In photographing, the head was slightly pulled out to 

 bring the beak into view. The dark patch of down on the crown is note- 

 worthy. 



Plate VII. 



Fig. 11. Young Tropic-bird. Age 12 hours; length 11.9 cm.; extent 

 11.2 cm.; wing 1.6 cm.; foot 2.8 cm.; bill 1.2 cm.; weight 25 grams before 

 receiving any food. Down white, excepting that the crown, regions of 

 wings, rump, and a patch on the back of the neck are tinged with dusky 

 or dull gray. The black skin is naked at the base of the beak, on the 

 lores, on the feet, and on the legs as far up as the heel. The beak and 

 tarsus are a light bluish slate color, the toes and webs of a very much 

 darker slate color. The eyes remain closed for a period of two days. 



Fig. 12. Young Tropic-bird. Age 4 days; length 12.7 cm.; extent 11.9 

 cm.; wing 1.8 cm.; bill 1.3 cm.; foot 2.8 cm.; weight 35 grams. The 

 bird at this age has its eyes open and is very alert and active. The down 

 of the breast is much shorter and thicker than that of other parts of the 

 body. The beak remains a bluish slate color like that of the freshly 

 hatched bird. The oil-gland tubercle is present, but is not yet functional. 



Plate VIII. 



Fig. 13. Young Tropic-bird with natural rock background. Age 

 8 days; length 16.1 cm.; e.xtent 16.7 cm.; wing 2.5 cm.; foot 3.6 cm.; 

 bill 1.4 cm.; weight 92 grams. No feathers have as yet appeared. The 

 legs in their relation to the body have a noticeably po.sterior position . 



Fig. 14. Young Tropic-bird. Age 15 days; length 20.1 cm.; extent 

 25.4 cm.; wing 3.5 cm.; foot 4.7 cm.; bill 2.0 cm.; weight 145 grams. 

 The various darker regions of the down mentioned in the description of 

 the freshly hatched young are still present, but do not seem to be so sharply 

 differentiated. There is very little down on the sides of the body beneath 

 the wings. In the scapular region have appeared the sheaths of the first 

 quill feathers. These sheaths with their downy tips measure 1 cm. in 

 length. The oil-gland tubercle is now well developed and has two open- 

 ings, through which the oil exudes when the gland is squeezed. There is 

 no down immediately around the tubercle, but a circlet of hair-like feath- 

 ers is appearing around its base. 



