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FORMS OF TAILS. 39 
cock of the plains; but in a few singular types (Tinamide) of the order 
Gallince, there are none, or only rudimentary ones. Among water birds the 
numbers vary so that they are usually of only generic, and sometimes only 
specific, importance. Those swimmers with long, well-formed tails, as 
the Longipennes, and particularly the gull family, and some of the ducks, 
have the fewest; here there are twelve, sometimes fourteen, rarely sixteen ; 
while those with short, soft tails have the most, as sixteen, eighteen, twenty ; 
and, as in the pelicans, twenty-two, or even twenty-four—the last being 
about the maximum, although in one genus of penguins (Apéenodytes) there 
are thirty-two or more. Swimmers again, furnish birds with no rectrices, 
the whole grebe family (Podictpide:) being thus distinguished. So rectrices 
run among birds from none to over thirty. The typical 
§ 70. Smarr or THE Tart, as a whole, is the ran. The modifications, 
however, are as many as, and greater and more varied than, those of the 
wing, at the same time that they are susceptible of better definition, and 
have received special names that must be learned. Taking the simplest 
case, where the rectrices are all of the same length, we have what is called 
the even, square or truncate tail, from which nearly all the others are simple 
departures in one way or another. A square, or nearly so, tail with the 
two central feathers long-exserted (§ 68) is common: we see it in all jaegers 
(gen. 280), in Momotus (gen. 112) and especially in Phaéthon (gen. 278). 
The most frequent departure from the even tail is by gradual successive 
shortening of the rectrices from the pair next the middle to the exterior 
ones; and this shortening is called gradation. Gradation is a generic term, 
implying such shortening in any degree. Precisely, it should mean shorten- 
ing each successive pair of rectrices by the same amount; say, each pair 
being half an inch shorter than the next. But this exactness is not often 
preserved. When the feathers shorten by more and more, we have the true 
rounded tail, probably the commonest form among birds: thus, let the grada- 
tion between the middle and next pair be just appreciable, and then increase 
regularly, to half an inch between the next to the outermost and the lateral 
pair. The opposite gradation, by less and less shortening, gives the wedge- 
shaped or cuneate tail; it is well shown in the magpie, where, as in many 
other birds, the central feathers would he called long-exserted, were all the 
rest of the same length as the outer. A cuneate tail, especially with narrow 
acute feathers, is also called pointed, in contradistinction to rounded, as in 
_ the sprig-tailed duck (gen. 253). The generic opposite of the gradated tail 
is the forked; where the lateral feathers increase in length from the central 
to the outer pair. The least appreciable forking is called emargination, and 
such a tail is emarginate; when it is more marked, as for instance, say an 
inch of forking in a tail six inches long, the tail is truly forked. The de- 
grees of forking are so various and intimately connected, that they are usu- 
ally expressed by qualified terms: as, “slightly forked,” “deeply forked,” 
ete. The deeper forkings are usually accompanied by a more or less fila- 
mentous elongation of the outer pair of rectrices: as in the barn swallow, 
