PHYLOGENY OF THE PALZOGNATHA AND NEOGNATH#. 163 
the rhachis bears about 6 or 7 pairs of rami. ‘The radii are slightly stouter, relatively. 
As in Casuarius, fila are minute and rare. 
The nestling-down of Apteryx (Pl. XLV. fig. 6) is easily distinguishable from that 
of the remaining Palwognathe. Like that of Dromeus and Casuarius, it has a 
well-developed shaft, but it differs from these in its greater length and in the very 
numerous rami. From Rhea and Struthio it differs entirely, in that, in these, the 
neossoptiles are umbelliform. 
The most striking feature perhaps of the nestling-plumage of Apteryx is its great 
length. In texture we appear to get three gradations. A. australis mantelli and 
australis very closely resemble one another and differ from the remaining species in 
that the feathers are coarser and slightly harsh to the touch. A. oweni and A. haasti 
stand at the other extreme and are peculiarly soft. Some individuals of A. australis, 
however, seem to stand between the two. 
A. haasti is the most markedly distinct of all. The feathers clothing the head, neck, 
and thighs are of a peculiarly downy character, recalling, in texture, the down-feathers 
on the breast of the adult Duck. On the back and breast they are of a peculiar 
“woolly” texture, resembling very strongly the intermediate plumage or pseudo- 
definitive feathers, (mesophyles of Palmer), which follow the prepenne in the Owls. 
There is no trace of an aftersnaft to these prepenne. 
The rami are closely set, very numerous (18 to 20 pairs), and moderately long. The 
radii are relatively short, and have the appearance of being formed of a number of 
short, laterally compressed joints, the dorsal and ventral angles of the anterior ends of 
which are produced forwards to form a pair of minute fila. 
In the length of the shaft and the great number of the rami the prepenna of Apterya 
stands alone amongst the Palwognathe ; moreover it is further peculiar in that it is not 
produced beyond the most distal radii into long filaments. 
A peculiarly interesting feature of the prepenne, and of the first definitive feathers, 
is that the latter do not thrust out the former, as they appear to do in all other known 
birds. Exactly how this is avoided is a point for further investigation. I hope to be 
able to explain this mystery shortly!. That this process of thrusting-out is: avoided 
can be still seen in a downy nestling of A. haastii in the Rothschild Collection. Here 
the first definitive feathers are about halfway through the skin, and show no trace 
whatever of a prepenna surmounting the tips, as do the other Palwo- and Neognathe. 
Furthermore, they are peculiar in that they are not invested by the sheath common to 
all developing feathers. ‘This appears to break away as soon as it reaches the surface 
of the skin. 
It may possibly turn out that this nestling-down plumage may represent preplume instead of prepennee ; 
this would account for their non-ejectment by the teleoptiles. The fact that plumule do not occur in the 
adult is of no importance, Zander [101] has described “ pinsel-artig” down-feathers in the embryo Ithea, but 
this is probably an error. 
