662 Mr. R. Shelford on the Pterijlosis of the 



sary to describe in some detail the distribution of the actual 

 feather-sheaths : those on the dorsal surface are transversely 

 banded with rufous and black, 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. 



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 &kin 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, j^erhaps, 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. hume rails {^g. 4:, pt. hum.). — This is much reduced in 

 size, and has lost its connection with the pt. spinalis 



