662 
Mr. R. Shelford on the Pterylosis of the 
sary to describe in some detail the distribution of tlie actual 
feather-sheaths : those on the dorsal surface are transversely 
banded with rufous and blacky in a manner suggestive of the 
colouring of the plumage of the young first-year Centropus; 
those on the ventral surface are whitish yellow, and much 
less far advanced in their development. 
j Distribution of the Feather-sheaths. 
Pt. capitis (fig. 4, p. 661, pt. cap.). —This is now a perfectly 
continuous tract covering the whole of the head, in¬ 
cluding the skin between the mandibular rami, between 
eye and nostril, and between ear-opening and the gonys 
of the jaw, areas which in Stage 2 were naked save for a 
very few delicate threads; the sheaths on the back of 
the head are the longest, the trichoptiles have dis¬ 
appeared almost entirely, being strictly limited to the 
sheaths on the crown and back of the head, and even 
these are much abraded; as already shown, they never 
were present between the mandibular rami; and it 
would, perhaps, be more reasonable to consider the 
feathers of this region as belonging to the pt. ventralis. 
It is to be noted that the upper eyelid bears a row of 
very short eyelashes (still enclosed in their sheaths), but 
these are not present on the lower lid, though a row of 
similar sheaths runs just below it. 
Pt. spinalis (fig. 4, pt. sp.).— Runs from the pt. capitis as a 
single tract to the level of the junction of coracoid and 
scapula ; it then abruptly ceases (fig. 4) to appear again 
at a lower level as a double tract, the two halves of 
which re-unite at a short distance above the pygidium 
and run down as far as the oil-gland papilla. The hiatus 
between the upper and lower portions of this pteryla is 
filled by trichoptiles so arranged that it is possible to 
see that the break in this feather-tract began in front 
of the point of bifurcation of the original trichoptilar 
tract. All the feather-sheaths bear trichoptiles. 
Pt. humeralis (fig. 4, pt. hum.).— This is much reduced in 
size, and has lost its connection with the pt. spinalis 
