772 BIRDS side of the structure with lumps of earth. Certain Warblers (Aedon and Tliamnobia) for some unascertained reason in variably lay a piece of snake s slough in their nests to repel, it has been suggested, marauding lizards who may thereby fear the neighbourhood of a deadly enemy. The clay-built edifices of the Swallow and Martin are known to everybody, and the Nuthatch plasters up the gaping mouth of its nest-hole till only a postern large enough for entrance and exit, but easy of defence, is left. In South America we have a family of birds (Furnariidce) which construct on the branching roots of the mangrove globular ovens, so to speak, of mud, wherein the eggs are laid and the young hatched. The Flamingo erects in the marshes it frequents a mound of earth some two feet in height, with a cavity atop, on which the hen, having oviposited, sits astride with dangling legs, and in that remarkable atti tude is said to perform the duty of incubation. The females of the Hornbills, and perhaps of the Hoopoes, submit to incarceration during this interesting period, the males immuring them by a barrier of mud, leaving only a small window to admit air and food, which latter is assidu ously brought to the prisoners. isional But though in a general way the dictates of hereditary n-ture instinct are rigidly observed by birds, in many species a remarkable degree of elasticity is exhibited or the rule of habit is rudely broken. Thus the noble Falcon, whose ordinary eyry is on the beetling cliff, will for the con venience of procuring prey condescend to lay its eggs on the ground in a marsh, or appropriate the nest of some other bird in a tree. The Golden Eagle, too, remarkably adapts itself to circumstances, now rearing its young on a precipitous ledge, now on the arm of an ancient monarch of the forest and again on a treeless plain, making a humble home amid grass and herbage. Herons also shew the same versatility and will breed according to circum stances in an open fen, on sea-banks or (as is most usual) on lofty trees. Such changes are easy to understand. The instinct of finding food for the family is predomin ant, and where most food is there will the feeders be s gathered together. This explains, in all likelihood, the ding associated bands of Ospreys or Fish-Hawks, which in )cie " North America breed (or used to breed) in large companies where sustenance is plentiful, though in the Old World the same species brooks not the society of aught but its mate. Birds there are of eminently social predilections. In Europe, excepting Sea-fowls whose congregations are universal and known to all we have perhaps but the Heron, the Fieldfare, and the Rook, which habitually flock during the breeding-season; but in other parts of the world many birds unite in company at that time, and in none possibly is this habit so strongly developed as in the Anis of the Neotropical Region, the Republican Swallow of North America, and the Sociable Grosbeak of South Africa, which last joins nest to nest until the tree is said to break down under the accumulated weight of the common edifice. 1 isitic In the strongest contrast to these amiable qualities is the parasitic nature of the Cuckows of the Old World and the Cow-birds of the New, but this peculiarity of theirs is so well known that to dwell upon it would be needless. Enough to say that the egg of the parasite is introduced 1 There are not many works on nidificatlon, for " Caliology " or the study of nests has hardly been deemed a distinct branch of the science. A good deal of instructive matter (not altogether free from error) will be found in Rennie s Architecture of Birds (London : 1831), and there is Mr Wallace s most interesting dissertation, " A Theory of Birds Nests," originally published in the Journal of Travel and Natural History (1868, p. 73), and reprinted in his Contributions to the Theory of Natural Selection (London : 1870). Mr Andrew Murray s and the Duke of Argyll s remarks on this essay are contained in the same volume of the Journal named (pp. 137 and 276). into the nest of the dupe, and after the necessary incuba tion by the fond fool of a foster-mother the interloper suc cessfully counterfeits the heirs, who perish miserably, victims of his superior strength. The whole process has been often watched, but the reflective naturalist will pause to ask how such a state of things came about, and there is not much to satisfy his enquiry. Certain it is that some birds whether by mistake or stupidity do not unfrequently lay their eggs in the nests of others. It is within the know ledge of many that Pheasants eggs and Partridges eggs are often laid in the same nest, and it is within the knowledge of the writer that Gulls eggs have been found in the nests of Eider-Ducks, and vice versa; that a Redstart and a Pied Flycatcher will lay their eggs in the same convenient hole the forest being rather deficient in such accommodation ; that an Owl and a Duck will resort to the same nest-box, set up by a scheming woodsman for his own advantage ; and that the Starling, which constantly dispossesses the Green Woodpecker, sometimes discovers that the rightful heir of the domicile has to be brought up by the intruding tenant. In all such cases it is not possible to say which species is so constituted as to obtain the mastery, but it is not diffi cult to conceive that in the course of ages that which was driven from its home might thrive through the fostering of its young by the invader, and thus the abandonment of domestic habits and duties might become a direct gain to the evicted householder. This much granted, all the rest will follow easily enough, but it must be confessed that this is only a presumption, though a presumption which seems plausible if not likely. EGGS. The pains bestowed by such Birds (incomparably the most numerous of the Class), as build elaborate nests and the devices employed by those that, not doing so, display no little skill in providing for the preservation of their produce, invite some attention to the eggs which they lay. This attention will perhaps be more cheerfully given when we think how many naturalists, not merely ornithologists, have been first directed to the study of the animal kingdom by the spoils they have won in their early days of birds nesting. Birds With some such men the fascination of this boyish pursuit nestiu has maintained its full force even in old age a fact not so muct to be wondered at when it is considered that hardly any branch of the practical study of Natural History brings the enquirer so closely in contact with many of its secrets. It is therefore eminently pardonable for the victims of this devotion to dignify their passion by the learned name of " OOLOGY," and to bespeak for it the claims of a science. Yet the present writer once an ardent follower of the practice of birds -ncsting, and still on occasion warming to its pleasures must confess to a certain amount of disap pointment as to the benefits it was expected to confer on Systematic Ornithology, though he yields to none in his Its us< high estimate of its utility in acquainting the learner with the most interesting details of bird-life without a know ledge of which nearly all systematic study is but work that may as well be done in a library, a museum, or a dis secting-room, and is incapable of conveying information to the learner concerning the why and the wherefore of such or such modifications and adaptations of structure. To some and especially to those who are only anatomists this statement may seem preposterous, but it is in truth no such thing. What engineer can be said to understand his business if he knows not the purpose to which the machines he makes are to be applied and is unacquainted with their mode of working? We may investigate tho roughly the organs of any animal, we may trace them from
the earliest moment in which they become defined, and