has been used relative to the mode by which they can accomplish so apparently arduous and difficult a task as forming their cells. Most, if not all of them, secrete a luminous fluid; and I believe the most general opinion is, that this luminosity is connected with or caused by phosphorus. Dr. Turton observes, that the three species of pholas (dactylus, our present one; parva, or small piddock; and candida, or white piddock,) are found in vast numbers in masses of rock, taken at the mouth of the river just below the town of Teignmouth in Devonshire; and he remarks, that "the philosophy of their natural history may probably be of no very difficult solution. The rock in which they are imbedded is a cementation of the finest sand and lime, and of so very soft a substance when first taken from its bed, as to be easily cut with a knife into any form, and sufficiently absorbent to afford moisture for the purposes of life and their peculiar action. The animals themselves abundantly secrete a mild phosphoric solution, as may be seen by its illuminating in the dark whatever is moistened with it, sufficiently powerful to decompose the rock by the slow contact of their gradually increasing bulk. The atmospheric air also seems to be occasionally necessary to this process, as they are always found in situations which are left dry for

a short period by the recess of the lowest tides, its oxygen perhaps serving by its union with this secretion to form a phosphorous acid. In confirmation of this belief, we have affixed them, when fresh taken, to a smooth piece of the same rock, by the frontal gape, occasionally moistening them with sea-water; and in a few days have found, that at the place of contact an evident waste of substance had been made by the decomposition of the lime and a deposition of sand in the finest grains. It may reasonably be supposed that all the borers of rock and wood, even the teredo, act in this manner by their peculiar and appropriate solvents.”*

I am afraid that this throws very little light on the subject. We have no proof that the luminous secretion of these animals is owing to phosphorus; and we know that many species which have the luminous, are quite destitute of the burrowing property; and, besides, the phosphoric acid would be about the worst agent which could be selected, because the phosphate of lime is insoluble in water, and I should fear, that when the carbonate was decomposed, the phosphate produced, instead of being carried off, would be deposited, and form a more intractable substance than the original chalk.

LETTER XV.

IN my last letter I referred you to some examples of Divine wisdom displayed in the contrivances and arrangements which are followed in the economy of nature, for adapting animals to that mode of life which they have been allotted to pursue; and as I consider this a most useful kind of study, I will offer you one more example of a similar kind, in a noted inhabitant of the ocean the whale.

Were our ideas of nature's productions not founded on strict and actual observation and research, we should, instead of possessing that satisfactory knowledge which every day is bringing to light, still wander in those mazes of error and conjecture which always characterise the infancy of science. How long, for instance, was the whale thought to be a fish? and by how many persons is it thought to be such even at the present time? Yet a fish it is not, any further than that it inhabits the water, and is of a fish-like shape. The true fish is cold-blooded,

has a heart composed of only one ventricle and one auricle, breathes by gills, and does not suckle its young. The whale has the very opposite of all these characters: its blood is hot, like that of man, quadrupeds, and birds; it has, like them, a double heart of two ventricles and two auricles; like them it breathes the atmosphere by lungs; and like them, also, it suckles its offspring.

There are various kinds of whales; as the cachalot, the broad-nosed whale, the white whale, the fin-fish, the grampus, porpoise, and several others. Some of them have formidable teeth, are very voracious, and great destroyers of fish and seals; while some are destitute of teeth, and prey only on animals of very small size. Such is the great Greenland or common whale (Balæna mysticetus), and to it I now intend to confine my remarks. This species grows to the length of seventy feet, and an individual sixty feet long will weigh seventy tons. It has, as I have said, no teeth; it has no arms for seizing its food; it cannot swallow any bulky object, for its œsophagus is barely wide enough to admit a man's arm. How, then, does it live? how is its vast bulk to be supported? The food of this enormous being consists of minute

LETTER XV.

Is my last letter I referred you to some examples of Divine wisdom displayed in the contrivances and arrangements which are followed in the economy of nature, for adapting animals to that mode of life which they have been allotted to pursue; and as I consider this a most useful kind of study, I will offer you one more example of a similar kind, in a noted inhabitant of the ocean- the whale.

Were our ideas of nature's productions not founded on strict and actual observation and research, we should, instead of possessing that satisfactory knowledge which every der ing to light, still wander in the