Embryos and Nestlings of Centropus sinensis. 665 



Inner aspect. — There are two rows of tect 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. Tlie egg- tooth has 

 disappeared and the foot is now exactly like that of the 

 adult^ the spur-like claw of the Ijallux 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 developmeut 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 empliasize 



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, couiparativt-ly 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-papillae have not advanced so far in developmeut, 



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- 



