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Show 351 MR. R. S. WRAY ON THE MORPHOLOGY [Apr. 5, larger proportions, and at the very earliest stages the remiges are distinguishable. At this stage the wing is quite rounded in section, there being no trace of the " ala membrana ;" the next feathers to appear are the t. majores (inferior), closely followed by the other ventral coverts, the other dorsal coverts meanwhile having appeared. At this stage (cf. Plate XXXII. fig. 1) the inferior major and median coverts are distinctly more on the dorsal half of tbe rounded edge of the wing than its ventral, but very quickly they become quite ventral, owing to the rapid growth of the remiges. This stage is quickly passed over, but sufficient is visible to show that these feathers are carried distinctly to the lower surface by inequality of growth (cf. Plate XXXII. figs. 2-4). The feathers resulting from these are the plumules seen in the wing of the Duckling, and of no use for flight. The wing of a Duckling reproduces in a great measure, allowing for specialized differences, the adult Ostrich's wing or the Rhea's; and these wings are survivals of the transition state of the wing, probably never having been used for flight, but having undergone special modifications of their own from that point. It is pretty clear the remiges of the Ostrich aud Duck's wing correspond, more so the Ostrich and Duckling's ; in the Ostrich we have but one row of ventral coverts, and in the embryo we get them most distinctly on the dorsal side. The Ostrich embryo figured (fig. 2 c, p. 351) shows the manus from the ventral surface; digits I., n., and in. being well developed; digit in. at its tip projecting beyond the general fold of the wing ; in fact there is a very complete webbed manus. The feathers seen (a', fig. 2 c, p. 351) are the row of ventral coverts, and lying over digit in. on its dorsal surface are two of this row hidden from sight by it. In the adult, one of these feathers grows over the distal part of phalanx 1 of digit m., owing to elongation of its quills ; here we have the dorsal position actually preserved in the adult. The wing of the Ostrich presents also a primitive condition especially in the cubital region, in that the " ala membrana " is not specialized as in the Carinatse, being in the intermediate condition of the Carinate embryo. Probably the feathers now representing the remiges and the principal coverts were more numerous in the primitive wing type, and have become restricted in number on the manus ; thus the Ostrich has 16, the Grebes 12, while most birds have only 11 primaries. Wing-Formula. The main facts with regard to the feathers of a bird's wing may be expressed as a formula. Denoting the metacarpo-digitals by Md, the metacarpals by m, the digitals by d, and expressing the number of feathers in each group by a number placed after (thus, six metacarpals, m 6), the cubitals by C, "quincubital," "aquincubital " by C5, we formulate the remiges 'Md 11 m6 db C5x*. The coverts are indicated by o, (3, y, for the t. majores, mediae, and minores respectively ; by placing a figure below the line, thus n2, * x = number of cubitals, which varies considerably in different groups. |