young animal has escaped from the egg, this ciliary motion is carried on, not alone by the fringe surrounding the mouth, but by cilia entirely surrounding the tentacles themselves, which whips up the supply of nourishment, and at the same time the proper aeration of the blood is effected. Whilst in the ova it probably is by this motion that the cell contents are converted into tissues and shell. From the twenty-sixth to the twenty-eight day, it appears actively engaged near the side of the cell, using all its force to break through the cell wall, which at length it succeeds in doing, leaving the shell in the ova sac, and immediately attaching itself to the side of the glass vase to recommence its ciliary play, and appear in a still more advanced stage. It is still some months before it grows to its perfect form. One of these snails may deposit from two to three of these ova-sacs a week, producing in the course of six weeks or two months from 900 to 1,000 young,"
It is to the Microscope then we owe this pithy description of the progress ab ovo, of a species allied to the common IAmnaa of our rivers.
We now turn to the Sea-slugs, whose shell, where it exists, is small and thin, slightly rolled and pearly white, and partially concealed by the animal; in Bullæa (Bubble shell,) we find an organ resembling the gizzard of a fowl, paved with calcareous plates capable of crushing the shell-fish on which it feeds. Many specimens of this shell we have obtained on the shore at Geelong. The Pteropoda our readers are seldom likely to meet with;—the Lamp-shell (Waldheimia) is not uncommon, attached by its pedicel to the oysters from Western Port, and its structure is worthy of examination; it belongs to Cuvier's 4th class, Brachiopoda, commencing the bivalve section, the animals comprised in which take their name from the ciliated arms on the side of the mouth, wherewith their food is obtained.
The well known bivalve shells of the Oyster and the Cockle are good types of the Conchifera, the animals of which are, with few exceptions, aquatic, and range at all depths on almost every coast and every clime. There are amongst them some burrowing shells, as the large white oblong Anatina (Lantern shell?) such splendid specimens of which are found in Corio Bay, a species of Solen, or Razor shell, and the borers are well represented by a Teredo which abounds on the piles at Williamstown.
The ability of many molluscs, especially the freshwater, to sustain life for a considerable time, is recorded in some remarkable instances; indeed it is probable that they become torpid in warm climates during the hottest and driest part of the year.[2] Mr. Gray, of the British Museum, received from this country a Pond mussel which had been more than a year out of water, and it still lived; some pond snails have been found alive after five years, although in the warm climate of Jamaica, and an individual of the Desert snail which had been affixed to a tablet in the British Museum in 1846, was found, on some suspicion having arisen as to his having made determined efforts to escape from confinement, still flourishing after being immersed in tepid water.[3]
A Cabinet of Shells is necessary for those who desire to study Conchology, and we may therefore hint, that to obtain specimens, perfect in shape and colour, dredging is the only good plan; but this may not be feasible, if so, the collector should wade amidst the rocks, examining the heaps of seaweed thrown on the sand after a storm, or carefully grope about all dark fissures, where many good species congregate, or are driven, nolens volens. Chitons and Limpets are only detached from the rocks by the aid of a strong bladed knife, as the former especially repel the air and water on all sides to produce a vacuum and so obtain a firmer hold, and they will sooner part with a portion of their shells than leave their places of attachment. Bivalves, and all live shells should be boiled and the soft parts removed when the valves separate or gape, but in doing this care should be taken not to injure the hinge, as it is often of material importance in the determination of genera; to preserve it therefore it is well to tie the shell round with some light thread. The operculum of Univalves must also be preserved, and should the contents of the shell at any time emit an unpleasant smell, a small quantity of chloride of lime will quickly and effectually remove it.
The arrangement of a collection of Shells is a mere matter of taste, much depending on the space that can be afforded to it. We who lead a somewhat nomadic life, prefer keeping the smaller species in small pill boxes, which can be purchased in nests at a trifling cost, the name of each species being carefully recorded on the lid; but a pair of each shell arranged on a cardboard, with the operculum glued down alongside, facilitates easy classification and subsequent examination.
We have not deemed it necessary to enter into a technical description of the columella, the hinge, and other portions of the shell, as this may be found in any elementary Work on the subject; to the amateur, Miss Catlow's little Manual will be of interest, but to the working Conchologist, we recommend Woodward's "Manual of the Mollusca," of which we need only say, that it is one of Weale's series, a sufficient testimony to its excellence.
1 ↑ Woodward's "Manual of the Mollusca.', p. 161.
2 ↑ Woodward's "Manual of the Mollusca."
3 ↑ Ann. Nat. History, 1860.
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