THE BXTHENAIi STErOTUEB OF BIEDS. J51 



swim, have an elongated powerful tail which is their main aid 

 in swimming ; but no bird whatever swims by its tail. Very 

 many climbing animals are assisted by a tail which is " prehen- 

 sile " or can grasp. Some birds (such as Woodpeckers) are 

 aided in chmbing by their very stiff tail-feathers. But no bii;d 

 has a tail which can grasp. No existing bird has a long tail in 

 the sense that a Cat has one. That part of a bird which 

 answers to the tail of a beast is a short fleshy, more or less 

 heart-shaped structure, which in the chicken is often called 

 the " parson's nose." Into it the long true tail-feathers are 

 implanted, and it also commonly bears on its upper surface, 

 at its root, a peculiar body known as the oil-gland, sometimes 

 called the uropygial gland or the elceodoeJion. The structure of 

 the bony basis of this true tail must, of course, be reserved for 

 description along with that of the rest of the endoskeleton. Here 

 we are alone occupied with its exterior and its epidermal appen- 

 dages. In the first place the oil-gland is composed of numerous 

 contorted tubes,which gather themselves together and unite more 

 and more till they open by one. or several pores on the surface 

 generally, on a little papilla. These tubes secrete within them 

 a greasy fluid, which exudes and can be pressed out from the 

 pore or pores. This gland is specially developed in aquatic 

 birds, which carefully anoint their feathers with its secretion, 

 the presence of which causes water so proverbially to " run off 

 a (Juck's back." The gland is often surrounded with a circlet of 

 feathers, the presence or absence of which serves as a distinctive 

 character of various species, and is by some anatomists con- 

 sidered important enough to define the great orders. 



The true feather-tail is formed by those generally well- 

 developed feathers which are inserted into the fleshy tail. These 

 feathers are called rectrices or steerers, and are, as a rule, 

 thoroughly firm and pennaceous, though generally the web of 

 the outer side of each feather is narrower than the other. The 

 rectrices are even in number, and there are generally twelve of 

 them. This number may, however, be diminished to eight or 

 raised to twenty or four-and-twenty, while the Penguins may 

 have two-and-thirty or even more. When the rectrices are 

 expanded it will be found that the central pair are inserted 

 highest up (most dorsaJly), one being higher in origin than the 

 other. The insertion will be found to follow on alternately — 

 the next to the median pair on one side being inserted above 

 the next to the median pair of the other side, and so on. These 



