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Show 216 DARWINISM CIIAP. become prn,ctically invisible amorw tho complex lightB <trrd shadows of the folin,gc they feed upon. . . In tho case of tho cuckoo, which bys 1ts ccms 111 the ll?Fits of a va,ricty of other birds, the eggs themselves a,rc ~HhJcct to considcra.l>lc va,rin,tions of colour, tho mo. t. common typ<', however rc cmblin<r tho. o of the pipits, wngtrul , or w;1rhlcr., in whos~ nests the~ arc most frequently laicl. . It al~o ofLcn lays in the nest of the hedge-sparrow, who c lmght hlnc cgus arc usually not at all nearly matc?cd, althot~gh they. :trc sometimes said to he so on the Contment. J t Js the opnnon of many ornithologists that each female cuckoo hy. the . ·mne Coloured co-O's and that it nsually chooses a no. t the owners of which biaby ' somewhat similar eggs, t ] JOU~ h t h'r s ~.s 1) y no means univcr ally the case. Although 1mcl. whH:h h~we cuckoos' eggs imposed npon them do not s em to neglcd them on account of any difference of colour, yet they prohthly clo so occasionally; and if, as seems probable, en,ch hinl's eggs arc to some extent protected by theh· harmony of colour with th eir surroundings, the presence of a larger ~tnd very difl'crently coloured eo·o· in the no 't might be d<tngerons, ancl le:tcl to tho dcstructior~~f the whole set. Those cuckoos, therefore, wlri ch most frequently placed their eggs among the kind}:; which they resembled, would in the long run leave mo.'t progcrry, an<l thus the very frequent accord in colour might have l>een brought about. . Some writers have sugge. ted tha,t the V<mccl colour~ of birds' eggs arc prim:trily clnc to the cfrcct of .·mr·on11<li11g coloured objects on the fem~tlc bird dnrin cr the pcriocl preceding incubation; and have cxpcnclccl mnch ingcrmity in suo-O'cstin()' the objects that may Jmvc can.·ecl the ccrg. of one bb b . 1 l ]) bird to be blue, another hrown, and another p111 c >Ut no evidence has been presented to prove that n.ny effects ·whatever arc produced by this cau. c, while there seem. no dif11 cu1Ly in accountincr for the facts by indivi<luctl va,ri;thility ancl the action of na.tt>u ral selection. The changcFi thn.t occm m. 1l 10 conditions of existence of birds mu. t Romctimes r ender 1 he coiLccalment less perfect than it mn.y once h~we been ; ancl when any danger a.rises from this cause, it may he met C'ithor 1 Seo A. II. S. Lucas, in P1·oceed·ings of Royal Society of lrictoTia, 18 7, p. 56. Vlll ORIGIN AND UHEH OF 'OLOUH. IN ANIMALS 217 by some change in tho colour of the cggFi, or in the strnctme or position of the n '~t, or hy the increa:cd care whiclr tho parents he. tow nporr th ccrcrfi. In thi: wn.y the Vttriom; divergences which ;now so often puzr.le U}:; may have arisen. Colow· as a llTeans of Rerognition. If we consider the habits n,nd life-histories of those a.nimn.ls which arc more or less <~'rcg;trious, compri:ing a large proportion of the herbi vorn,, some ca,nrivora, rmd. a considerable number of a] l ordcrB of birds, we sh<tll sec th<tt ~t means of ready recognition of its own kirrd, at a clist.rncc or during rapicl motion, in the du.-k of twilight or in partial cover, must he of tho greatest advantage n,ncl often lead to the preservation of life. Animals of thifi kind will I rot usnally receive a stranger into their midst. -While they keep to(l'cthcr they arc generally saJe from attn.ck, but a solitary stra.ggler hecomcs an C<tsy prey to tho enemy; it is, therefore, of the highest importance that, iu such a case, the wamlcrer should have every facility for discovering its companions with certainty at any distance within the mng of vi.·ion. Some means of Oitsy recognition mnst be of vital importance to the young and inexperienced of each flock, and it also enables the sexes to recognise their kind <tnd thn. avoid the evils of infertile eros. cs; arHl I am inclined to llClievc tha.t its necessity ha,s ll <t<l :.t more wide. prcct(l i11flnencc in determining the eli versitics of aninml coloration tlmn any other cause whatever. To it may prohahly he imputed the singular bet thn,t, whereas bilateral symmetry of coloration i · very frequently lost among domesticated nnimn,ls, it almost nnivor-. ·;tlly prevails in a sta,tc of 1raturc ; for if the two side. of an arrimal were 11rrlikc, n.nd the divcr}:; ity of color:ttion among domestic animals occurred in a wild st<tte, easy recognition would he impossible among numerous closely n.l1icd forms.! 1 Professor Wm. H. Brower of Yale College l1as sl10wn tl1at the white mark~; or th spots of dome~ticatod animal:< ar · rarc•ly symmetrical, llllll1avo a tendency to appear more frequently on tl1e left side. Tllis h; the ca."e with horses, cattle, dogH, and sw in e. Among wild animal .. 1he sk unk varies ·onsidembly in the amount of white ou tl1e ho(ly, and this too was fountl to he usually greatest on the loft si(le. A close oxallli nation of Jllllnerous stripccl or spotted species, as tigers, leopards, jaguars, zebras, etc., showed tllrtt the bilateral symmetry waH HOt exact, aHhough the general ofl'cct of the two sides |