THE COMMON IS WALLOW. 91 



the toe which corresponds to our great toe (the one directed backwards), without moving any of the 

 others. In the Swift, however, whenever the great toe (the hallux)* is fully flexed, it is impossible 

 that the other toes should remain opened out, because the two muscles, which act on one and the 

 other, are bound together by a tendinous band. 



"In the Swallow, the Sparrow, and most singing birds, the number of feathers in the tail is twelve. 

 In the Swifts and Humming-birds the number is always ten another important difference. In the 

 Swallow also, as in all the passerine birds, there is a slender muscle running through the thin 

 triangular membrane of the wing, between the arm and the fore-arm, which is quite peculiar in the 

 manner of insertion or attachment, no other birds possessing the same arrangement. In the Swift, this 

 muscle terminates in quite a different manner, here again resembling the Humming-birds exactly. 



" Taking these several characters into consideration, and realising how little they are susceptible, 

 on account of their deep-seatedness, to the influence of slight external changes in the mode of life of 

 the species, we are inevitably driven to the conclusion that their weight is overwhelmingly greater 

 than that of the superficial similarity, which is so readily brought about by the similarity of the 

 circumstances under which the two species are accustomed to live, and that the resemblances between 

 them are, so far as their constitutions are concerned, dependent only on the fact that they both have 

 with different pedigrees arrived at a superficial similarity in contour, because they subsist exclu- 

 sively on the same food." 



The Swallows, then, may be subdivided into two sub-families, called respectively the Rough-winged 

 Swallows and the Smooth-winged Swallows, both of which sub-families are represented in the Old 

 and New Worlds. 



THE FIKST SUB-FAMILY OF THE HIRUNDINIDJE. THE EOUGH- WINGED 

 SWALLOWS (Psalidoprocnince). 



These birds are called "rough "-winged on account of the serrated edge which is found attached to 

 the outer margin of the first primary. So strongly is this indicated that on pressing the thumb along 

 the edges of the feather a distinct feeling of a saw-like sensation is produced. Curiously enough, this 

 feature only obtains in the males, and as far as has been noted at present, is found in two genera, 

 Psalidoprocne^ in Africa, and 8telgidopteryx\ in the New World. Of the South African Rough- 

 winged Swallow Mr. Layard gives the following brief notice : " This little Swallow first fell under my 

 notice on the ' Keurboom's River,' Knysna district, where I saw it apparently breeding in holes in 

 the banks, but was unable to investigate its doings more closely. I found it abundantly in the forest, 

 hawking after flies over pools, frequently dipping into the water, and perching on the overhanging 

 boughs in clusters of six or eight, to dry themselves. Their habit of perching is noted by Mr. Cairncross, 

 who writes, ' This bird flies about very much like a bat (this resemblance also occurred to me when I 

 saw it) amongst thick forests, and is generally more visible in rainy, heavy weather ; but I have 

 never seen or heard of their breeding here (Swellendam). They remain here after the winter has set in. 

 Sometimes I have seen them roost on trees at the bottom of my garden, where I shot the specimen 

 sent.'" 



THE SECOND SUB-FAMILY OF THE HIRUNDINID2E. SMOOTH- WINGED SWALLOWS. 



To this group of birds belong by far the larger number of the Swallows, including also the Martins 

 and the Sand Martins. It may not be out of place here to note the points by which the three English 

 species of Swallows may be distinguished by an ordinary observer. On the wing, the Swift is very 

 Swallow-like in appearance, but may be told by its large size, extremely rapid flight, long wings, and 

 entirely black plumage. The Sand Martin breeds in holes of banks, and is the smallest of the three 

 English Uirundines, being pale brown above and white below. The common Martin builds a mud 

 nest under eaves of houses or barns, like the Swallow, but may easily be told on the wing by a con- 

 spicuous white band across the lower back. The forked tail is not perceptible in the Martin when in 

 flight, but is very easily seen in the common Swallow, especially in the male birds, in which the 

 elongated outer tail feathers are very conspicuous at all seasons of the year. When they first arrive, 



* See figure of Skeleton of Eigle, Vol. III., p. 241. 



t V'oAi's, a pair of shears ; Upoicvr), a mythological character. J oreAyi's, a scraper; nrepov, a wing. 



