or at most three or four ova, has its own proper globule of jelly, contained within a skin or pellicle of the greatest tenuity, and which isolates it from the rest.* The annexed figure (Fig. 70) exhibits this disposition as we see it in

Fig. 70.

the spawn of the Periwinkle (Littorina littorea); and you perceive also that the minute embryos are already covered each with its shell, so that any metamorphosis they undergo is early and speedily completed.

A few species of these phytivorous Gasteropods are viviparous, the spawn being lodged in the branchial cavity until the young are fitted for a separate existence; and we find some oviparous and some viviparous species in the same Thus the common Periwinkle (Littorina littorea) genus. has the economy of the first, and the Littorina rudis that of the second. The Paludina vivipara affords another illustration of the same fact; and the foetal shell of this, as Swammerdam ascertained, is armed with crystalline spines arranged in regular rows on the whorl, while the mature shell is even and destitute of armature. It is almost the only instance known amongst Mollusks of the embryo shell exhibiting an exterior structure different from the adult. Spallanzani affirms that young individuals of Paludina vivipara taken from the mother, and kept always in a state of isolation, yet produced in due time young, a fact from which you are not to infer, with him, their monoecious nature, which anatomy disproves, but that a single impreg

The embryo has the same rotatory motion in the ovum of these and other Mollusca as that described in the spawn of the bivalves. See Carus as translated in Zool. Journ. iv. 257.

nation is sufficient for at least two generations, as we know to be the case with the Aphides or Plant-lice.*

The zoophagous Gasteropods, living usually in deeper water, where the spawn is more exposed to forage, enclose their eggs in capsules of a horny texture, and often so curiously connected and contrived that nowhere will you find finer displays of the Creator's preserving care over all his works. The ova, while passing from the body, and while still in the oviduct, are included within a glairy excretion prepared in an accessory glandular apparatus, and which is moulded into a coriaceous pouch of very variable figure according to the species. It is either single or compound. In the former case, every pouch, as it is extruded, is attached by the animal, one by one, to the rock chosen for the precious trust; in the latter case, the cluster of oviferous receptacles is expelled in one common mass: and when you are told that this is frequently much larger than the shell of the parent, you may wonder how this can be? And so did Dr. Job Baster. "I have often wondered," he says, "how a univalve could lay an ovary exceeding, by five or six times, its own size. But the explanation is obvious enough, for it is proportionably small, and of a soft glutinous consistence on its first deposition; it grows after its expulsion, and keeps pace with the growth of the ova and young, and at the same time hardens to a more solid and coriaceous texture. I have seen the receptacles of the Purpura lapillus when they were less than a line in height, and their colour was also then much darker than it is at maturity." The process of laying is very well described by a correspondent of Sir E. Home's as observed by him in the Turbinella pyrum. "A friend of mine," says Sir Everard, "saw the female shed her eggs; a mass, apparently of mucus, passed along the deep groove in the lip of the shell in the form of a rope, several inches in length, and sunk to the bottom: this rope of eggs, enclosed in mucus at the end last discharged, was of so adhesive a nature, that it became attached to the rock, or stone, on which the animal deposited it. As soon as the mucus came in contact with salt water, it coagulated into a firm membranous structure, so that the eggs became enclosed in membranous chambers, and this connected nidus, having one end fixed and the other

*M. Alex. de Nordmann found that some Nudibranchial genera laid fruitful ova without the individual having had any society with another of its species. Ann. des Sc. Nat. (1846) v. 136. Being of androgynous structure, this fact is more readily explained than it is in Paludina. Alder and Hancock's Nudibr. Mollusca, iii. fam. 3 pl. 7 and 8.

A A

See

loose, was moved by the waves, and the young in the eggs had their blood aerated through the membrane, and when hatched they remained defended from the violence of the sea till their shells had not only been formed but had acquired strength."*

These egg-capsules are so diversified in their forms and mode of aggregation,† that M. A. Lund, a learned Danish zoologist, has reduced them into classes and orders in a manner well calculated to impress distinctly their diversity on the memory. The arrangement is as follows:

CLASS I.

THE MASS OF EGG-CASES IRREGULAR. (The egg-cases form in their aggregate masses of indeterminate shape.)

ORDER i. Egg-cases coherent: The cases are attached to and upon each other.

Family 1. The egg-case opening by a fissure of the margin.

2. The egg-case opening by a circular aperture furnished with a membra

nous lid.

ORDER ii. Egg-cases adherent: The cases are attached to a common basal membrane, by which they are rooted.

Family 1. The egg-case opening by a fissure of the margin.

2. The egg-case opening by a circular aperture furnished with a membranous lid.

* The egg-cases sessile, or directly attached to their common base.

a. Tubiform.

** The egg-cases pedunculated, or attached to their common base by a pedicle.

*Comp. Anat, iii. 396,

a. Egg-shaped.

b. Cup-shaped.

c. Funnel-shaped.

The various Tubularia represented by Esper in his "Pflanzenthière," in plates 11 to 16, and 18 to 26, are the egg-cases or embryo sacs of zoophagous mollusca.

CLASS II.

THE MASS OF EGG-CASES REGULAR. (The egg-cases form in their aggregate masses of a determinate figure.)

ORDER i. Egg-cases coherent.

ORDER ii. Egg-cases adherent; the cases are attached to a common body serving as an axis.

* The egg-cases attached all round the

axis.

** The egg-cases attached along one side

of the axis.

a. Sessile.

b. Pedunculated.†

66

conca

I shall now describe a few of these egg-cases, or merated nidus," as Sir Everard Home calls them. Those of our common Whelks belong to M. Lund's first family. That of the Buccinum undatum Ellis names "Sea washballs," for they are "used by the sailors as soap to wash their hands;" but our fisher-lads of the north countrie call them "fyke," because, with the dried powder of them, they torment their fellows by slyly insinuating it between the skin and clothes, when it raises a very intolerant degree of itching. The common nest is composed of numerous coriaceous pouches of a compressed globular shape, united, by a strong ligament, into a roundish mass, which, in size and general appearance, may be aptly compared to the nest of some humble-bees. Each pouch, "about the size of half a large pea," contains about four young, and these, when about to be hatched, have already four whorls, and exhibit, in tolerable perfection, the character of the adult shell.‡ The nidus of the Fusus antiquus is more regular and curious (Fig. 71): when of full size it forms an obtuse cone about three inches in height and two in diameter, attached firmly by a broad basis to rocks in deep water. This cone is made up of a number of large pouches, joined together by a strong cartilaginous band or skin in a regular manner: each cell is shaped something like the human nail, convex outwardly and concave on the inner side, with a strong horny outer coat slit along the upper edge, but the aperture so narrow

+ Ann. des Sc. Nat. (1834) i. 93.

Ellis Corallines, 84, pl. 32, b, B. Baster Opusc. Subs. i. 14. tab. 5, fig. 2. J. E. Gray in Charlesw. Mag. Nat. Hist. i. 248.

that it affords entrance to nothing excepting the water which is necessary to aerate the growing young (a).* Within this pericarp, and only very loosely connected with it, there is

a bag of a similar form (b), but everywhere close, and of such a thin and pellucid membrane that it presents no obstacle to the influence of the oxygenating medium. At first its contents are fluid and granular, but soon opacities are to be discovered in several places, and ultimately from two to six young are developed in each pouch, which can only make their way out, at the appointed time, by a rupture or dissolution of the inner bag. Still more singular are the concamerated nests of many exotic zoophagous Gasteropods. Here is the figure (Fig. 72) of a portion of one which seems to have afforded Mr. John Winthrop the subject of the following notice :-" Moreover," he says, in describing some curiosities he had sent to the Royal Society, "there are some of the matrices, in which those shels are bred, of which the Indians (American) make the white wampanpeage, one

* Baster says that it admits neither air nor water-" quæ aeris aquæque marinæ ingressum arcet, sed quæ exitum foetu maturo ex ovis concedit.". Opusc. Subs. i. 37. tab. v. fig. 3.