Embryos and Nestlings of Centropus sinensis. 665 
Inner aspect .—There are two rows of teet rices marginales on 
the manus, one row on the cubitus. There is no 
hypopteron. 
The nestling now appears to be remarkably short-necked; 
i. e. } the neck has not grown in length in proportion to the 
increase in size of the head and trunk. The egg-tooth has 
disappeared and the foot is now exactly like that of the 
adult, the spur-like claw of the hallux being very noticeable. 
Comparison with smaller examples of the same stage 
reveal but few differences : these are :—the greater length of 
the trichoptiles; the absence of feather-sheaths at the angle 
of the jaw (as in Stage 2); the weaker development of the 
pt. ventralis, the point of bifurcation of its two main streams 
commencing much higher up, and thus affording an illustra¬ 
tion of the method by which the pt. colli laterales of Stage 2 
become confluent with the pt. ventralis; and, finally, the 
exact correspondence of the arrangement of the wing- 
feathers with the arrangement of the trichoptiles in Stage 2, 
fig. 3, p. 659. 
In order completely to understand the changes which take 
place during the growth of the nestling of an early stage to 
the nestling of Stage 3, it is necessary again to emphasize 
the fact that a trichoptile is merely an enormously prolonged 
feather-sheath, enclosing at its base, beneath the skin, a 
feather-papilla; as the feather-papilla grows, that part of the 
trichoptile which ensheathes it must perforce grow too, but 
the elongated part which, comparatively early in embryonic 
life, broke through the skin need not, and in fact does not, 
grow, except in the matter of length, and that only to a 
small extent, owing to its outwardly pushing base; finally, 
the actual feather-sheath makes its appearance, pushing 
before it its trichoptilar appendage, which has now become 
abraded to a considerable extent. In certain areas these 
feather-sheaths appear contemporaneously, but in others the 
feather-papillse have not advanced so far in development, 
and the sheaths do not push through to the exterior till 
some time after the young bird has left the nest; further, 
these feathers are invariably degenerate semiplumes ; not- 
