AYES. 



159 



The brain, in Birds, offers tlie same general characters as in the rest of the Ovipara ^ 

 nut is distinguished by its very considerable proportionate size, which often even sur- 

 passes that of this organ in the Mammaha. It is principally on the tubercles analo- 

 gous to the corpora striata that this volume is dependent, and not upon the 

 hemispheres, which are very small and without convolutions. The cerehellum is 

 tolerably large, and almost without lateral lobes, being principally formed by the 

 vermiform process. 



The trachea of Birds has its rings entire ; at its bifurcation is a glottis, most usually 

 furnished with peculiar muscles, and named th.e lower larynx; it is there that the voice 



rlty, — tlie otlier of immaturity ; the first liavin^ usually mure decided 

 ;iLiJ i;uiitriistuii cn[uurs ; the bcfuiid being cuniparatively sombre, with 

 fainter or more blended eoloiira, which however arc commonly broken 

 into various strcalts or Hjiots, and oiber difFcrent niotlliiifs ; where the 

 liitter condition, however, becomes permanent, the variegntions of the 

 adult bird are in ijeneral more distinctly defined ; tlius a beautiful 

 Himnialayan Thrush (^Tnrdtis fVhilei) , wV\c\y occasionally Blrnys into 

 Kurope, retains the mottling of the doraal plumage peculiar to the 

 unnioulted young of oilier Thrushes, but the colours of those mottled 

 fsHtUers are much more finely brought out ; in like manner the disiiiLCt 

 transverse bars on the adult plumage of the Bush-shrikes {Thamno- 

 p/ii/iis) and those on certain Woodpeckers (Coluptes), respectively 

 ripresent the more indistinct markings of the nentling dress of the 

 '.rdiiinry Shrikes (L'uiiiis) and certain other Woodpeckers {Chrysu- 

 ;j/'j7«.f), which barred plumage Is succeeded in Che latter by an ^dult 

 (<arb devoid of those markings : this increased distinctness is however 

 !eas apparent in siune cases, as in that uf the Bittern of North Ame- 

 rica, tlie adult markings of wliich correspond, feather by feather, {their 

 Intensity being but incunsidernbly enhanced,) with those of the im- 

 mature Dwarf-bitterns already referred to. 



Accordingly, thpn, it is in the first plumage of Birds that the nffinity 

 of allied groups is ordinarily most apparent, as is analogously the case 

 with the young of animiils in general (the distinctions of all esscu- 

 tMliy allied groups of which emitinue to decrease till they disappear 

 successivelv, aa we ascend to the embryo) ; and the same remark 

 nppMcH, as might be anticipated, to the shupe and structure of the 

 leathers, etiULlly with their colouring. Thus, the nestling garb is 

 alviiiys much leas firm tlmn that subsequently attained [ and those 

 f. atliers which are iicumiiiiite in the adult are rounded, or but slightly 

 nan owed, in the young, anti ia general betome gradually more 

 .l.iiigated and pointed at each successive moult, till tliey have ac- 

 r|i]ircd ihcir final shape and developenient : the dorsal feathers of the 

 c.uiiinon Heron, and clothing plumage of the Stnrling, may be cited 

 in exemplification. Tn this respect, also, as with their colouring, the 

 featliers of some species, compared with those of others proximately 

 allied, are speeifically arrested at various stages of developement : the 

 H.iult plumage of the Bitterns represents io lliis particular the imma- 

 ture garb of the Herons generally ; and in the weakness of texture of 

 the doraal feathers, equally with their mottled markings, the mature 

 livery of the luntkocivcliX corresponds with the nestling dresa of the 

 majority of other Birds of the Thrush tribe. 



It should be remarked that in some cases where the typicil plumage 

 is finally attained, this is only after a series of moultings more or less 

 numerous, each successive stage of which may or may not present a 

 nciirer approximation to it in different species ; it being thus assumed 

 (iradually, or abruptly ; and, in such cases, it is generally acquired by 

 the male sex sooner than by the female, where both ultimately arrive 

 at it. In the Kuropean Oriole, the male alone attains the typical garb, 

 but not before its third or fourth change of plumiigc, when it is 

 assumed abruptly, or nearly so; in the Dwarf-bitterns, the mate 

 (icijuires its fiiial livery at the first moult, tlie female not before the 

 third or fourth moult, presenting an intermediate garb in the mean 

 uliilc, which is ultimately exchanged for the same livery as that of its 

 mate. The amount of constitutional vigour tends to determine the 

 period at which the more advanced condition of plumage is obtained, 

 in the ratio of the average period required for its assumption: thus, 

 we perceive little or no irregularity in those instances where the 

 typical dress is gained at the first renewal, but considerable irrcgii- 

 iarity where the period of its assumption is ordinarily protracted ; and 

 it would seem that in the latter case the females are more apt to 

 aiquire ultimalcly the most advanced livery, than in those instances 

 H here the male alone regularly obtains it at the first moult ; though, 

 a.s there is always a tendeticy on the part of vigorous females to throw 

 ')ui the masculine attire, it maybe that this appareJit difference arises 

 aimply from the fact of such females being liable to escape notice, 

 from their consequent similarity to tlie other sex inducing a belief 

 that tticy belong to it, and so precluding furth 

 species thus usually presenting a 



mage, we have seen females of the common Redstart, Linnet, Redpole, 

 Red-backed Shrike, and Scaup Pochard, which could not be distin- 

 guished externally from males ; and all of them conluined eggs in the 

 ovarium. 



As the assumption of the typical plumage, then, in species wherein 

 it is tardily acquired, is especially dependent on the amount of con- 

 stitutional vigour, it follows that captive Birds should generally arrive 

 more slowly at their final livery, than those individuals which arc 

 unconfincd ; and it might be predicated, also, that instances of capti\c 

 females assuming tlie male plumage, in those species wherein the 

 females ordinarily differ from the males, w.iuld be of comparatively 

 uufrequent occurrence. Such are accordingly the facts : but it requires 

 to be noticed, that any effectual injury to the ovarium, or other cause 

 of sterility, also occasions female Birds lo throw out the masculine 

 livery (just aa the Doe, mentioned at p. 137, ^''ith one schirrous ovary, 

 developed an antler on the same side), this fact being very commonly 

 noticed in Pheasants and domestic Poultry. On the other hand, how- 

 ever. It is still more remarkable that a male bird, analogously injured, 

 will sometimes even moult hack from the typical plumage to that pro- 



irked sexual diversity of pU- 



the nestling garb of the latter, (or, in other words, that its plumage 

 presented the same analogy with that of the House Sparrow which 

 the common Bunting's plumage does to that of its congeners): the 

 affinity of such a S[iecies to the Tree Sparrow, both seses of which 

 exhibit at all ages a style of colouring corresponding to that peculiar 

 [0 the adult m:de of the House Sparrow, would be rendered intelli- 

 gible by the mutation incidental to the latter, even though no actual 

 similitude were traceable between the plumage of the Tree Sparrow 

 and that of the imajiined species. There are numerous groups, then, 

 the relationship of which may be at once recugiiiied on the principle 

 here indicated. 



Among those species which retain their first plumage till the second 

 autumn, ita aspect undergoes considerable variation in some, from 

 different eausts. Thus, in the Osprey, Gannet, and some others, the 

 upper parts are for a while conspicuously spei kled with terminal white 

 spots, on a dark ground-colour ; which spots gradually disappearing, 

 as the terminal edges of the feathers are naturally shed, leave the 

 back uniformly dark-coloured and plain. In certain other groups, as 

 in some Harriers [CiTrvs), an actual change of colour takes place in 

 the feathers, to a variable extent. 



In those species of Birds which undergo a double moult, the sexes 

 are ge^crally similar, or nearly so, in both states of plumage, and 

 lie winter dress ; and even the summer and winter liveries 

 all cases differ, as may he observed in the Tree Pipit 

 ■horem). Wlicrc tlie contrary prevails in both sexes, the 

 heir first down, are subject to possess the colouring of the 

 ner garb, as noticeable in the common Guillemot and 

 and, in the plumage which succeeds the down, to resemble 

 the mature winter dress, or to present a combination of the two, 

 which is not uncommon— particularly among the small waders, which 

 subsequently attain their proper winter clothing plumage by a moult 

 towards the close of autumn. When the breeding livery of the male 

 and female differs, the same law prevails aa in single-moulting Birds. 

 We have not space to enter more minutely into detail. — Ed. 



