Imágenes de páginas
PDF
EPUB

The Uria grylle, Lestris catarractes, pomarinu, and parasitica, have two eggs and two breeding spots. The Uria Brunnichii and troile, Puffinus arcticus, and Procellaria glacialis, have one egg and one spot. The Uria alle, Alca tordu, and Mormon fratercula, have but one egg and two breeding spots.

The Phalaropus cinereus, and Platyrhinchus, lay four eggs, and have but two breeding spots. The Sterna arctica, Larus glaucus, marinus, and tridactylus, have sometimes three, sometimes two eggs, but constantly only one breeding spot.

These spots are not entirely meant to supply the place of a nest ; they are, therefore, not invariably in an inverse ratio to the building impulse. Certainly, the species which want these spots, as the Sula and Curbo, build a nest ; most of those, also, which are provided with them build no nest, as the Phalaropus, Uria, Alca, Morindu, Puffinus, Sterna, Lestris, Procellaria ; but the genus Larus have breeding spots and build nests.

Their presence is therefore merely a proof of the development of the pairing impulse, but is not to be considered as synonymous with the laying of eggs or hatching. Birds pluck out these feathers before even they have joined their mates, and without being certain of breeding that year. Therefore I have found them in May, in individuals of the Lestris catarractes, and Procellariu glacialis, which were so far out at sea, and removed from the breeding places of the species, that I had good cause for reckoning these barren birds, which pass the summer without breeding. They also exist in the single individuals of the Lestris parasitica, which flock about together.

After hatching is over, these bare spots are very quickly again covered with feathers. All traces of them have disappeared in August and September, when the young of some species are not yet fledged.

Analysis of the Stony Pericarp of the Lithospermum officinale.

By Captain CHARLES LE HUNTE. (Communicated by the

Author.) This may be considered one of the most remarkable substances in the vegetable kingdom, its properties, mechanical and chemical, are those of a mineral, rather than that of a vegetable. The seeds resemble small, pear-shaped, porcelain beads; they are very hard, difficult to break, and have a high polish. When heated, they at first become black; but they do not shrink, nor does a white heat change their form, in the slightest degree; it destroys, however, their lustre, and renders them, when the vegetable matter has been consumed, whiter than they were originally. Before the blowpipe, small pointed fragments of the pericarp may be partially fused ; but this requires a good heat.

To determine the nature and quantity of the earthy constituents, the pericarps were carefully separated from the enclosed seeds, and exposed to the action of dilute muriatic acid; a violent effervescence immediately commenced, which did not entirely cease for upwards of two hours. At the end of twelve hours, the acid liquor was decanted, and the pericarps were well washed. Their appearance was not in the least changed; when dried, at a moderate heat, they still retained their original lustre. The acid liquor was found to contain a great deal of lime, a very little phosphate of lime and oxide of iron, with traces of potash and magnesia, which were separated in the usual manner.

The pericarps were then heated to destroy the vegetable matter, which it is exceedingly difficult to effect ; but, notwithstanding the intense heat employed, the form of the fragments was not changed by it, they merely lost their lustre, and became very white. When the vegetable matter was entirely consumed, they were again treated with muriatic acid, and left in a warm place for several hours. The acid took up a very little phosphate of lime and oxide of iron. The matter insoluble in the acid, was fused with carbonate of soda, and found to be pure silica. The analysis was repeated, and the composition of the substance appeared to be very uniform. The following is the result:

43.70 16.5

Carbonate of Lime,
Silica,
Vegetable matter, small quantity of phosphate of lime and

oxide of iron, with traces of potash and magnesia,

39.8

100

The silica appears to form the polished surface of the seeds. As the acid acted upon the vegetable matter of the pericarps, and took up a little phosphate of lime and oxide of iron, that could not be weighed accurately, it was scarcely possible to estimate the quantity of carbonic acid that they contained, from the loss of weight caused by the effervescence. I found it a little greater than it ought to have been, on the supposition that the whole of the lime was in the state of carbonate ; and I did not think it necessary to have recourse to a more delicate mode of ascertaining its quantity, for I had no reason to suspect

the

presence of any other salt of lime, excepting a small quantity of the phosphate. When the dilute muriatic acid was applied to the pericarps, the effervescence was brisk ; but they appeared to offer some resistance to its action ; and when they were not allowed to remain in contact with it, for at least twelve hours, the silica always contained a little lime. Nitric acid, which acted more powerfully upon the vegetable matter, dissolved the lime speedily, the fragments became very thin, and the siliceous coating alone was left ; but, in this case, it was quite impossible to make any calculation for the carbonic acid.

An examination of a larger quantity of these seeds might afford some interesting results; and the whole plant is worthy of attention. I may remark, that they had been collected a year when the analysis was made.

On the Vitality of Toads enclosed in Stone and Wood. By the

Rev. W. BUCKLAND, F.R.S., F, L. S., F.G.S., and Professor of Geology and Mineralogy in the University of Oxford. Communicated by the Author.

In the month of November 1825, I commenced the following experiments with a view to explain the frequent discoveries of toads enclosed within blocks of stone and wood, in cavities that are said to have no communication with the external air.

In one large block of coarse oolitic limestone, (the Oxford oolite from the quarries of Heddington) twelve circular cells were prepared, each about one foot deep and five inches in diameter, and having a groove or shoulder at its upper margin fitted to receive a circular plate of glass, and a circular slate to protect the glass; the margin of this double cover was closed round, and rendered impenetrable to air and water by a luting of soft clay. Twelve smaller cells, each six inches deep and five inches in diameter, were made in another block of compact siliceous sandstone, viz. the Pennant Grit of the Coal formation near Bristol ; these cells also were covered with similar plates of glass and slate cemented at the edge by clay. The object of the glass covers was to allow the animals to be inspected, without disturbing the clay so as to admit external air or insects into the cell. The limestone is so porous that it is easily permeable by water, and probably also by air ; the sandstone is very compact.

On the 26th of November 1825, one live toad was placed in each of the above-mentioned twenty-four cells, and the double cover of glass and slate placed over each of them and cemented down by the luting of clay; the weight of each toad in grains was ascertained and noted by Dr Daubeny and Mr Dillwyn, at the time of their being placed in the cells; that of the smallest was 115 grains, and of the largest 1185 grains. The large and small animals were distributed in equal proportion between the limestone and the sandstone cells.

These blocks of stone were buried together in my garden beneath three feet of earth, and remained unopened until the 10th of December 1826, on which day they wereexamined. Every toad in the smaller cells of the compact sandstone was dead, and the bodies of most of them so much decayed, that they must have been dead some months. The greater number of those in the larger cells of porous limestone were alive. No. 1, whose weight when immured was 924 grains, now weighed only 698 grains. No. 5, whose weight when immured was 1185 grains, now weighed 1265 grains. The glass cover over this cell was slightly cracked, so that minute insects might have entered ; none, however, were discovered in this cell; but in another cell, whose glass was broken, and the animal within it dead, there was a large assemblage of minute insects, and a similar assemblage also on the outside of the glass of a third cell. In the cell No. 9, a toad which, when put in, weighed 988 grains, had increased to 1116 grains, and the glass over it was entire ; but as the luting of the cell within which this toad had increased in weight was not particularly examined, it is probable there was some aperture in it, by which small insects found admission. No. 11 had decreased from 936 grains to 652 grains.

When they were first examined in December 1826, not only were all the small toads dead, but the larger ones appeared much emaciated, with the two exceptions above mentioned. We have already stated that these probably owed their increased weight to the insects which had found access to the cells and become their food.

The death of every individual of every size in the smaller cells of compact sandstone, appears to have resulted from a deficiency in the supply of air, in consequence of the smallness of the cells, and the impermeable nature of the stone; the larger volume of air originally enclosed in the cells of the limestone, and the porous nature of this stone itself (permeable as it is slowly by water and probably also by air) seems to have favoured the duration of life to the animals enclosed in them without food.

It should be noticed that there is a defect in these experiments, arising from the treatment of the twenty-four toads before they were enclosed in the blocks of stone. They were shut up

and buried on the 26th of November, but the greater number of them had been caught more than two months before that time, and had been imprisoned altogether in a cucumber frame placed on common garden earth, where the supply of food to so many individuals was probably scanty, and their confinement unnatural, so that they were in an unhealthy and somewhat meagre state at the time of their imprisonment. We can therefore scarcely argue with certainty from the death of all these individuals within two years, as to the duration of life which might have been maintained had they retired spontaneously and fallen into the torpor of their natural hybernization in good bodily condition.

The results of our experiments amount to this; all the toads both large and small inclosed in sandstone, and the small toads in the limestone also, were dead at the end of thirteen months. Before the expiration of the second year, all the large ones also were dead ; these were examined several times during the second year through the glass covers of the cells, but without removing them to admit air; they appeared always awake with their eyes open, and never in a state of torpor, their meagreness increasing at each interval in which they were examined, until at length they were found dead ; those two, also, which had gained an ac

« AnteriorContinuar »