is the egg of the Dog-fish, a small species of shark. Some of the sharks produce their young alive; others bring them forth enclosed in these cases, which are deposited by the parent in shallow parts of the sea, along the shore. They are oblong, convex at the sides, semitransparent, of a clear yellowish horn-colour, and with a firm horny texture. From each of the four angles issues a long tendril, which coils round sea-weeds or any

other fixed body near which the egg may be deposited, and of which it can take hold, and thus anchored it defies securely the tossing of the waves, awaiting its proper season for being hatched. There is an opening at each end of the purse, through which the sea-water finds its way to the prisoner enclosed within, and at length the young shark makes his exit through one of these, at the end nearest to which his head is placed.* Another anomalous object commonly found, consists of a number of firmly membranous little bladders, each

* See Yarrell, Hist. of Brit. Fishes, 2nd edit., vol. ii. p. 487, &c.

about a quarter of an inch in breadth, flat on the inside, and convex on the outside, adhering together in regular order by their expanded margins: the whole forming a body which looks like a wasp's nest. In March or April, each of these little membranous sacs, which is found empty and pierced with a hole a month or two later, contains a soft yolk, in which is gradually formed a young univalve mollusc, whose shell begins to take its proper shape before he emerges from the membranous

egg. These froth-like masses are indeed the eggs of the large whelk (Buccinum undatum), which inhabits deeper water, beyond the recess of the tide, where it attaches these masses of eggs to rocks and stones, from which they often become loosened and are cast up in rough weather, as are also the whelks themselves, whose dead shells we frequently meet with

on

shore. Somewhat similar

eggs are produced by other allied species, the forms and localities differing in each. The eggs of a common species, with a coarse, white shell, sometimes banded with brown and yellow (Purpura lapillus), are frequently seen attached to small stones, on the sides of rocky hollows. These are little oblong urns, each raised on a short stalk, fixed to a circular expanded base, and pierced by a hole. They generally

EGGS OF MOLLUSCA.

33

occur in groups of ten, twenty, or more together. The egg clusters of other univalve mollusca are equally curious, but they are commonly found in deeper water, or may more properly be noticed when speaking of the rocks. These animals are much

more frequent on rocky ground, and naturally prefer the stability of a fixed nursery, such as a rock affords, to deposit their eggs. But one species of sea-snail (Natica monilifera), with a polished, light-brown shell, elegantly marked with dark streaks and spots, either leaves its egg-cluster loose,

in sandy places, or attaches it so carelessly that it frequently becomes loose. These egg-clusters are really very curious and elegantly formed objects, which must have often attracted the notice of a rambler, who felt puzzled to know what they were. They are firmly gelatinous, or of the consistence of gristle; transparent, or nearly so; slightly coated with fine sand, and in shape resemble the hoof of an animal. When dry, they look not unlike pieces of thin

NATICA MONILIFERA.

Scotch oaten bread. Their surface is marked with little hexagonal spaces, which define the eggs. But what is

D

most to be admired in the structure, is the form of the curves which the hoof-like body assumes, which fit it for lying on loose sand, without becoming deeply buried in it. It is difficult to make this peculiar form clearly understood by mere description, but I have said sufficient to identify the object.

or

The Mollusca which inhabit sandy shores habitually, and in the greatest numbers, are not the Univalve or snaillike families, whose organization is more adapted for crawling over rocks and sea-plants, where also they find their appropriate food; but another very distinct group of shell-coated animals, called CONCHIFERA,* TESTACEOUS ACEPHALA, which are capable of living buried, sometimes to a considerable depth in the sands. Some of this class of animals are indeed confined to rocky places, anchoring themselves in various ways permanently in a position, either on a rock or on the stem of a seaweed; or forming hollow chambers by burrowing in the solid rock itself; but the majority of species inhabit sandy places, and their shells continually meet us on the sandy shore, while the living animals may be detected buried along the margin of the retreated tide. The shell, in all these animals, consists of two principal, saucershaped pieces, more or less perfectly covering the body of the animal, and united together by a more or less complex hinge, opened by a highly elastic ligament. The Scallop and the Common Cockle offer well-known examples of such a shell:-the first having a simpler structure, both in the hinge and in the animal, is better

"General Outlines of the Animal Kingdom, by Professor Rymer Jones," p. 375, et seq.

adapted for explaining the general features of organization, while the latter may be instanced as affording modifications of structure which adapt it to the peculiar locality to which it is confined.

On opening the valves of a living scallop we perceive, within the margin of the shell, a soft membrane, which lines the whole of the inner surface, and encloses the body of the animal as in a cloak, open in front through the centre; so that a curtain fringed round the edge with innumerable slender filaments, hangs from each valve of the shell. This membranous envelope, which is called the mantle, exists, though under many modifications, in all the mollusca, and indeed is one of their most essential parts. It is by means of this organ that all the shell-coated tribes cover themselves with the beautiful shells which are objects of so general admiration. The thickened margin of the mantle is furnished with glands which secrete both colouring matter and carbonate of lime. From the latter material, deposited in cellular substance derived from the animal, the shell is gradually formed by constant additions to its margin; while the colouring matter, poured in at the same time, gives to the outer surface all the peculiar markings which characterize each kind. The outer coat of the shell is therefore entirely the work of the margin of the mantle. Its increase in thickness is an after-process, effected by the general surface of this organ, which throws off layers of pearly substance, and adds them continually, one after another, to the inner surface of the shell. Thus as the shell increases in size, its walls grow in thickness. In the Scallop,