these are its chosen haunts, and that it more rarely builds in chimneys than in England *. In Sweden it is the same, and hence it is called the Barn-swallow (Ladu swala); while in the south of Europe, where chimneys are rare, it builds in gateways, porches, and galleries, or against the rafters of outhouses, as in Virgil's time:

Garrula quam tignis nidum suspendat hirundo +."

In 1829, we observed about a dozen of these nests, suspended from the rafters of a large coach-house at the village of Hockheim, on the Maine .

When a chimney is selected, it seems to prefer one where there is a constant fire, most probably for the sake of warmth. "Not," remarks White, "that it can subsist in the immediate shaft, where there is a fire, but prefers one adjoining to that of the kitchen, and disregards the perpetual smoke of that funnel, as I have often observed with some degree of wonder. Five or six or more feet down the chimney, does this little bird begin to form her nest about the middle of May, which consists, like that of the windowswallow, of a crust or shell composed of dirt or mud, mixed with short pieces of straw to render it tough and permanent; with this difference, that whereas the shell of the former is nearly hemispheric, that of the latter is open at the top, and like half a deep dish this nest is lined with fine grasses and feathers, which are often collected as they float in the air. Wonderful is the address which this adroit bird shews all day long in ascending and descending with security through so narrow a pass. When hovering over the mouth of the funnel, the vibrations of her wings, acting on the confined air, occasion a rumbling like thunder. It is not improbable that the dam submits to this inconvenient situation, so low in the + Geor. iv. 306. $ J. R.

* J. R.

the yolk, which intestine was inferred without proof to have existed previous to fecundation. M. Dutrochet, on the contrary, found that the intestine enters the yolk by a development extended by successive processes over the whole periphery of the yolk.

The chemical constituents of these several parts of the egg are as follows. The shell consists principally of carbonate of lime, similar to chalk, with a small quantity of phosphate of lime and animal mucus. When burnt, the animal matter and carbonic acid are separated, the first being reduced to ashes or animal charcoal, and the second dissipated; while lime, mixed with a little phosphate of lime, is obtained. The white is without taste or smell, of a viscid glary consistence, readily dissolving in water, coagulable by acids, alcohol, and water heated to 165° Fahrenheit. When it has been thus coagulated, it is no longer soluble in either cold or hot water, and acquires a slight insipid taste. The experiments of Dr. Bostock show that it is composed of 80.0 parts of water; 15.5 of albumen; and 4.5 of mucus; exhibiting, besides traces of soda, benzoic acid and sulphuretted hydrogen gas. The latter we observe on eating an egg with a silver spoon to stain it with blackish purple, by combining with the silver, and forming sulphuret of silver. The yolk possesses an insipid, bland, oily taste, and when agitated with water forms a milky emulsion. When long boiled it becomes a granular, friable solid, yielding by expression a yellow, insipid fixed oil. Its chemical constituents are water, oil, albumen, and gelatine. In proportion to the quantity of albumen, the egg boils hard. The oil of the yolk is soluble in sulphuric æther.

An important part of the egg which we have not hitherto named is the air-bag (folliculus aëris),

placed at the obtuse extremity, and well described by Dr. Paris. "The external shell," he says, "and the internal membrane by which it is lined, constitute the parietes [walls] of the cavity, whose extent in the recent egg scarcely exceeds in size the eye of a small bird: by incubation, however, it is extended to a considerable magnitude. That its most essential use is to oxygenate the blood of the chick, in my opinion there can be no doubt; but to establish completely the truth of such a theory, it is necessary to discover the nature of the air by which it is inflated, and which has hitherto remained unexamined." From experiments made to ascertain this point Dr. Paris concludes that "before incubation it contains atmospherical air. No other chemical change takes place in the constitution of the air, than a small inquination with carbonic acid. It gains by incubation an increase of volume, which takes place nearly in the ratio of 10 to 1. I must here remark, that its extent does not increase equally in equal successive portions of time, but observes a rate of progression, which is accelerated as the latter stages of incubation advance: it seems, however, to arrive at its maximum of dilatation a few days previous to exclusion of the animal.

"The same apparatus exists in the eggs of all birds, and contains a similar air: its capacity, however, does not seem to vary either with the size of the egg or of the bird to which it belongs; but I think I have discovered a beautiful law by which its extent is modified. I have uniformly found, as far as my contracted inquiries have led me, that the folliculus aëris is of greater magnitude in the eggs of those birds which place their nests on the ground, and whose young are hatched, fledged, and capable of exerting their muscles as soon as they burst from their shell, than in the eggs of those whose nests are

and feathers. Of the small nests, built in the corners, I could find only two in tiers, and I inferred that they were the property of young pairs, as they were not so compactly built as the larger ones

The ingenious masonry of the swallows, which we have thus described from competent authorities, is very similar to that of some of the mason-bees (Megachile muraria, &c.); but, the bees, though they sometimes mix stones with their clay, never, so far as we know, chop up straw and hay, like the swallows, in order to strengthen their fabric, probably because their salivary cement is a more efficient binder. A mason-bee also makes a separate nest, smoothly polished within, for every egg she deposits, and covers it in with a coping of masonry; but the swallow leaves her clay wall rough on the inside, because the soft bedding which she afterwards lays there would render it a waste of time to be very nice. Moreover, as the female bee always dies before her eggs are hatched, she requires to be more careful in providing for their security than the swallows, who affectionately take care of their offspring till they can forage for themselves †.

* Montbeillard, Oiseaux.

† See Insect Architecture, p. 34, &c.

having too free a communication with the atmosphere, by which its powers are exhausted: it is to obviate such an effect that the horticulturist, taught only by experience, covers it with a glass, by which means he limits the extent of its atmosphere, and consequently decreases its respiration, transpiration, and the inordinate actions which would prove fatal to it*."

*Linn. Trans. x. 309.