xiii PHYLUM CHORDATA 351 



1. EXAMPLE OF THE CLASS.- -THE COMMOX PJGEOX (Columba 



lima, var. domcstica). 



The Common or Domestic Pigeon is known under many varieties, 

 which differ from one another in size, proportions, coloration, 

 details in the arrangements of the feathers, and in many points of 

 internal anatomy. The Pouters, Carriers, Fantails, and Tumblers 

 may be mentioned as illustrating extreme forms. All these 

 varieties have, however, been produced by artificial selection, 

 that is, by breeders selecting, generation after generation, the 

 Birds which most nearly attained to some artificial standard of 

 perfection, breeding from them alone, and killing off the inferior 

 strains. The ancestral species from which the domestic breeds 

 have in this way been evolved, is the Rock Pigeon (Columlia livi") 

 which is widely distributed in the Palsearctic and Oriental regions. 

 The following description refers especially to the Common Dovecot 

 Pigeon. 



External Characters. In the entire Bird (Fig. 963) the 

 plump trunk appears to be continued insensibly into the small, 

 mobile head, with its rounded brain-case and prominent beak 

 formed of upper and lower jaws covered by horny sheaths. The 

 head, neck, and trunk are invested in a close covering of feathers, 

 all directed backwards and overlapping one another. Posteriorly 

 the trunk gives origin to a number of outstanding feathers which 

 constitute what is ordinarily called the tail. From the anterior 



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region of the trunk spring the wings, also covered with feathers, 

 and, in the position of rest, folded against the sides of the body. 

 The legs spring from the hinder end of the trunk, but, owing to 

 the thick covering of feathers, only the feet are to be seen in the 

 living Bird, each covered with scales and terminating in four digits 

 (dg. 1' dg. 4'), three directed forwards and one backwards. 



In order to make a fair comparison of the outer form with that 

 of other craniate types it is necessary to remove the feathers. When 

 this is done the Bird is seen to have a long, cylindrical, and very 

 mobile neck, sharply separated both from head and trunk. The 

 true tail is a short, conical projection of the trunk, known as the 

 uropyginm, and giving origin to the group of large feathers (ret.) to 

 which the word " tail " is usually applied. On the dorsal surface 

 of the uropygium is a papilla bearing on its summit the opening 

 of a large gland, the oil-gland (o.gl.), used for lubricating or 

 " preening " the feathers. 



The wings show the three typical divisions of the fore-limb, 

 upper arm, fore-arm, and hand, but the parts of the hand are 

 closely bound together by skin, and only three imperfectly-marked 

 digits, the second (dg. 2) much larger than the first (dg. 1) and 

 third (dg. 3), can be distinguished. In the position of rest the 



