TECTRICES 95 1 



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 projpatacjium 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 tedrices aversse 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 gi-adually pushed over to the ventral side, so as to 

 assume the position of LoAver 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. see. fig. p. 608) connecting their bases.^ 



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 in a 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 discoveiy it is easier to understand the relations 

 between remiges and tectrices majores and tectrices media; in the Ratitsa and 

 Sphenisci, and moreover to arrive at a possible explanation of tlie development 

 of the remiges as such. Struthio and the Oscines have only one row of inverted 

 Lower coverts ; PJica 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 intennediate 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 Rhea and 

 the Oscines. 



