Embryos and Nestlings of Centropus 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 
pterylae. 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. 
par. — 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- 
