FOKMS OF TAILS. 39 



cock of the plains; but in a few singular types {^Tinamidce) of the order 

 Gallince, there are none, or only rudimentary ones. Among water birds the 

 lunnbers vary so that they are usually of only generic, and sometimes only 

 speeitio, impcu'tance. Those swimmers Avith long, well-formed tails, as 

 the Lomjipennefi, and particular]}' the gull family, and some of the ducks, 

 have the iewest ; here there are t\velve, sometimes fourteen, rarely sixteen ; 

 while those Avith 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 maxiuium, although in one genus of penguins [A/jtenodyfet^} tjjiCVG 

 are thirty-two or more. Swimmers again, furnish birds with no.rcc'xrices, 

 the whole grebe family i^Podicipidce) being thus distinguished. So rectrices 

 run among birds from none to over thirty. The tijjyiccd 



§ 70. Shape of the Tail, as a ^vhole, is the fan. The moditieations, 

 however, are as many as, and greater and more varied than, those of the 

 wing, at the same time that they arc susceptible of better definition, and 

 have received special names that nurst be learned. Taking the simi)lest 

 case, where the rectrices are all of the same length, we have what is called 

 the even, xquare or Inmca/e tail, fi'om which nearl}' all the others are simjde 

 departures in one way or another. A square, or nearly so, tail with the 

 two central feathers long-exserted (§ t)8) is common : we see it in all jaegers 

 (gen. 2b0), iu Momotus (gen. 112) and especially in J'/iacl/ion (gen. 278). 

 The most frequeut 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 gradallon. Gradation is a generic term, 

 implying such shortening in ;uiy 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 olten 

 preserved. When the feathers shorten by inore and more, we have the true 

 rounded tail, probabl}' the commonest form among birds : thus, let the giada- 

 tion between the middle aud 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 /e.s.s and /e.s.s shortening, gives the u-edf/e- 

 shaped or cuneate tail; it is well shown in the magpie, where, as in many 

 other birds, the central feathers would be 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 geueric 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 ernargination, and 

 such a tail is emarginute ; when it is more marked, as for instance, say an 

 inch of forking in a tail six inches long, the tail is \vu\y forlxed. The de- 

 grees of forking are so various and intimately connected, that they arc usu- 

 ally expressed by qualitied terms: as, " slightly forked," "deeply forked," 

 etc. The deeper forkings are usnullij accompanied by a more or less fila- 

 mentous elongation of the outer pair of rectrices : as in the barn swallow, 



