TECTRICES 951 
and very obliquely by those of the Middle series, which are inserted 
each between a remex and its corresponding Greater covert. The 
Lower coverts arise from the fleshy part of the wing, and the 
marginals clothe the propatagiwm or anterior part of the wing to 
which they are restricted. 
The Greater and Middle rows of Lower coverts have their con- 
cave surface downwards, thus agreeing with the remiges and with 
the Upper coverts. They are the fectrices averse of Sundevall, and 
the explanation of the apparent anomaly they present has been 
given by Wray, who found that they are originally situated on the 
dorsal side of the wing, but that, during the growth of the embryo, 
they are gradually pushed’ over to the ventral side, so as to 
assume the position of Lower coverts (Proc. Zool. Soc. 1887, 
pp. 343-357). This shifting is probably initiated through the 
greater development of the feathers on the upper surface which 
become the remiges, and to the formation of the tendinous band 
(elast. sec. fig. p. 608) connecting their bases.1 
The overlapping of wing-coverts presents some curious features. 
Feathers are said to overlap proximally when the inner vane or web 
of any one is overlapped by the outer vane of its proximal or inner 
neighbour. This is the case with (1) all the remiges, as well as in 
the so-called bastard wing, (2) all the Greater coverts, both Upper 
and Lower, (3) the Upper Middle coverts of the hand, and frequently 
those of the arm, (4) those of the PARAPTERON (p. 684) or upper 
humerals, and (5) the marginals, both Upper and Lower. On the 
other hand, feathers overlap distally when the inner vane covers the 
outer vane of the one next to it. Such a row of feathers therefore 
seems to run ina direction opposite to that of the remiges and Greater 
coverts, and of this kind are (1) all the Middle and Lesser Lower 
coverts, (2) the feathers of the HYPOPTERON (p. 454), (3) very fre- 
quently the Lesser Upper coverts, and (4) in many birds the Middle 
Upper coverts. The number and position of these distally-over- 
1 Owing to Wray’s ingenious discovery it is easier to understand the relations 
between remiges and tectrices majores and tectrices medi in the Ratitx and 
Sphenisci, and moreover to arrive at a possible explanation of the development 
of the remiges as such. Struthio and the Oscines have only one row of inverted 
Lower coverts ; Rhea and the Sphenisci have none. In the last there are more 
than 30 rows of little scale-like feathers on each surface of the wing, the largest 
of them not being, as in most Birds, the last series, but the last series but one on 
the hand, and the second and third last on the dorsal side of the forearm. 
This suggests the probability that in the Penguins no rows of feathers have been 
turned ventrally round the posterior margin of the wing, which is to say, that 
these birds retain a condition which in the others is characteristic of embryonic 
life. Struthio possibly represents an intermediate stage, in which only one row 
has been turned ventrally, unless indeed a reduction from several rows to one row 
has taken place, and such a reduction has probably been effected in Ahew and 
the Oscines, 
