666 On Embryos and Nestlings of Centropus sinensis. 
withstanding their late appearance and degenerate character, 
the trichoptiles appertaining to them appear at the same 
time as, and are quite indistinguishable from, the others. 
The arrangement of the trichoptiles is then prophetic of the 
adult pterylosis, at least so far as the dorsal surface is con¬ 
cerned, and a combination of the diagrams of the dorsal 
view of the nestling of Stage 2, and of the ventral view of 
Stage 3, fig. 5, will represent nearly exactly the adult ptery¬ 
losis. The almost total absence of trichoptiles from the ventral 
surface I would explain thus :—The embryo lies in the egg in 
a strongly curved position, the dorsal side being the convex 
surface, the ventral side the concave; further, the curve is 
so circumscribed that almost every part of the ventral sur¬ 
face is in close contact with another part, and it is difficult 
to see where room could be found for a dense mane of 
trichoptiles such as is found on the dorsal surface, hence 
must occur a retardation in the outward growth of these 
structures along the area later occupied by the pt. ventralis. 
But when the young bird hatches out, it lies or moves about 
in the nest on its chest and stomach, subjecting these parts 
to a considerable amount of friction ; and as I have already 
shown that the dorsal trichoptiles become much worn though 
subjected to much less friction, it is perhaps not unfair to 
conclude that ventral trichoptiles will not be developed to 
any extent if they are liable to be worn away on or soon 
after their first appearance. Still, this is the merest specula¬ 
tion, since I am unable even to hazard an opinion as to the 
function of the trichoptiles : the nestling is certainly not 
rendered inconspicuous by them, and as, moreover, it is con¬ 
cealed in a deep nest, invariably built in dense undergrowth, 
it is presumably independent of such protective devices; and 
still more unlikely is it, that the young of so highly spe¬ 
cialized a group of birds as the Cuckoos should retain the 
primitive body-clothing, and this quite apart from the fact 
that both the distribution and structure of these trichoptiles 
point the way to deductions of an opposite nature. 
The pterylosis of the adult Centropus sinensis differs in 
one or two details from that of C. celebensis as described by 
