Embryos and Nestlings o/Ceiitropus sinensis. G61 



stage; it will at once be seen that the changes in appearance 

 that have occurred are both striking and important. In the 

 first place, the horny sheaths of some of the definitive feathers 

 carrying at their extremities the trichoptiles have broken 

 through to the exterior in certain well-marked areas : in the 

 second place, the pt. ventralis is now almost completely 



Figs. 4, 5. 



Fig. 4. — Dorsal aspect of Stage 3, showing the changes in the form of the 

 pterylse. Compare with fig. 1. 



Fig. 5. — Ventral aspect of Stage 3. The pteryla ventralis has now com- 

 pleted its growth. Compare with fig. 2, p. 655. 



Explanation of the lettering, 

 apt. coll. lat. = apterion colli laterale. 

 2)ar. = parapteron. 

 pt. cap. = pteryla capitis. 

 pt. caud. = „ caudalis. 

 pt. hum. = ,, humeralis. 

 pt. sp. = „ spinalis. 

 pt.f. = ,, femoralis. 

 pt. V. = „ ventralis. 



plotted out by feather-sheaths which, however, do not bear 

 trichoptiles at their extremities; and, thirdly, the areas 

 previously occupied by trichoptiles are still so occupied, 

 except where they have been encroached on by the newly 

 appeared feather-sheaths. The reason and significance of 

 these changes will be explained later^ meanwhile it is neces- 



