1901.] EVOLUTIOTf OF PATTERN IN FBATHBRS. 321 



although at first sigbt they appeav somewhat puzzling. The vermi- 

 culatedforin of pattern is very common among them, and in some 

 extreme cases, e. g. Asio otus, the whole feather seems to be mottled 

 indiscriminately, while in others, e. g. Scojjs, the vermiculation is 

 confined to the bars, or the area that should be covered by bars. 

 The Barn Owl, however (Plate XX. fig. 5) forms a good connecting 

 link for this vermiculated pattern, which has broken off from the 

 main line of evolution at an early stage. Fig. 4 shows the earliest 

 beginnings of it in the typical series. It will be noticed on refer- 

 ence to Plate XX. fig. 5 that all the markings are confined to the 

 tip of the feather, and that no distinct bars can be made out in the 

 vermiculation itself ; but if this vermiculated part be omitted from 

 consideration for a minute, we have clearly the stage very nearly 

 approaching fig. 3. 



Plate XX. fig. 6 represents the feather from the breast of a 

 young Scops Owl showing the vermiculation restricted to the bar 

 area. 



The Burrowing Owl does not bear out the statement that the 

 upper parts (where any difference exists) show a higher form of 

 evolution than the underparts. In this case the feathers of the 

 back are of the form shown in fig. 7, while the underparts are 

 barred. This need not, however, occasion much difficulty, for it 

 will be readily seen that the habit of this bird being to sit at the 

 mouth of its burrow, the underparts would be the most exposed, 

 and consequently those on which laws causing evolution would tend 

 to act most vigorously. 



The large order of Passeres is that to which we may next turn. 

 The British Thrushes as a series show us clearly the lines of evo- 

 lution. In the young of Turdus viscivorus, we find on the back 

 the last bar alone persistent, so that according to the table they 

 may be considered as forming a highly evolved race. The indi- 

 vidual feathers on the back of the young Missel Thrush exhibit 

 considerable variation : some of them show the bar as V-shaped, in 

 others it is straight, while in some the dark colour is no longer to 

 be found on the rhachis and is only found in two longitudinal bars 

 along the centre of the vane on either side. In White's Thrush 

 this stage persists in the adult, but the tip always remains as a 

 bar, more or less crescentie, whereas in the Missel Thrush the 

 feathers have become self-coloured. 



The young of the Song-Thrush (Plate XX. figs. 10 & 11) is similar 

 to that of the Missel Thrush, except that evolution has gone slightly 

 further as it is much more nearly self-coloured. On the wing-coverts 

 all trace of a bar has disappeared, the two longitudinal stripes, 

 representing the original arms of the V-shaped bar, have covered 

 the whole vane, the rhachis being alone left of a yellowish colour 

 vdth A-shaped markings of a similar colour at the tip. The feathers 

 still show traces of the dark V-shaped bar ; but a tendency to slur 

 over the stages is shown, so that they are not distinct as in the 

 Missel Thrush. 



As regards the underparts, they are never in advance of the upper, 

 Proc. Zool. Soc— 1901, Yol. II. No. XXI. 21 



