upon

found the same modified by the site to which it was attached, so as to have become like a riband fully eight inches in length and ths of an inch broad; and this was elegantly wrapped round the lower part of the stem of the Tangle, to which it adhered by one margin only. The riband was of a white colour, and within its substance the ova, in countless numbers, were neatly arranged in regular cross spiral lines.* The spawn of the Eolis papillosa forms an elegant spiral chain of a milk colour and several inches long, twisted itself and constricted at regular intervals, so as to resemble a necklace made of bugles. The ova, as in the dioecious phytophagous Mollusca, are very numerous. Mr. C. Darwin calculated those of a Doris native of the shore of the Falkland Islands. "From two to five eggs (each 10ths of an inch in diameter) were contained in a spherical little case. These were arranged two deep in transverse rows, forming a riband. The riband adhered by its edge to the rock in an oval spire. One, which I found, measured nearly twenty inches in length and half in breadth. By counting how many balls were contained in a tenth of an inch in the row, and how many rows in an equal length of the riband, on the most moderate computation there were six hundred thousand eggs. Yet this Doris was certainly not very common; although I was often searching under the stones I saw only seven individuals." This is a striking illustration of a fact very general amongst invertebrate animals,-their numbers bear no proportion to the exceeding multitude of their eggs, as if the law given to man to plenish the earth was in them restricted merely to the perpetuation of the species.

The terrestrial genera are greatly less fertile in ova. The Helix pomatia, according to Lister, deposits only about fifteen eggs; and in our common snails they do not exceed from thirty to fifty. In general they are separated from each other, though deposited in little heaps; but a large species of native slug which inhabits cellars has the eggs,

There is a figure of the spawn of a Doris in Baster, Opusc. Subs. i. tab. x. fig. i. C. D. The spawn of Pleurobranchus is very similar. Audouin and M. Edwards, Litt. de la France, i. 134.

+ Voy. Adv. and Beagle, iii. 258. The ova of Doris tuberculata, "on a moderate computation, cannot be less than fifty thousand."-ALDER and HANCOCK in Ann. and Mag. N. Hist. xii. 235. But its young "have myriads of enemies in the small infusoria, which may be noticed with a powerful microscope hovering round them, and ready to devour them the instant weakness or injury prevents their keeping in motion the cilia, which serve both for locomotion and defence. Let them cease to move, a regular attack is made and the animal is soon devoured; and it is interesting to observe several of these scavengers sporting in the empty shell as if in derision at the havoc they have made."-PEACH in Ann. and Mag. N. Hist. xv. 446.

which are large, strung together like a necklace by a narrow thread. Swammerdam has noticed the peculiarity in other species. "Some snails," he says, "lay their eggs up and down on the ground, others tie them all together like a chain."-The form of the egg is spherical or oval; and their colour is usually bluish-white or milk-white unstained by any markings. The eggs, however, of the Helix bicarinata and H. purpurea are of a beautiful yellow, a colour which also distinguishes those of the Agathinæ indigenous to Africa and its islands.* In size the ova vary as much as do the creatures from which they come: in the common snail (Helix nemoralis) they are not larger than mustard-seed, and their necessary minuteness in such a diminutive Mollusk as Helix pygmæa must render them invisible to our eye; but those of the Bulimus hæmastomus, Lamk. are almost as large as a pigeon's, and with a shell equally hard and calcareous. The arboreal species of Bulimus which inhabit the Philippines "deposit their eggs in little clusters on the trees, between two leaves which the animal manages to curl up, one upon the other, so as to form a receptacle for their protection; and so far as Mr. Cuming's observations go, they are all soft, like snake's eggs, with the single exception of the B. mindoroensis, in which instance the eggs are calcareous, deposited upon a leaf in parallel rows, each standing perpendicularly on end, attached at the base by a glutinous substance." + The earthborn tribes exhibit less or no artifice, beyond that little which leads them to conceal their fruit in a sort of subterranean nest, or lay them under stones or clods of earth, or hide them in moss or amidst decaying leaves, where they hatch secure from the evil influence of the sun and of the summer's drought.

Being laid, the eggs even of the land Mollusks rapidly acquire an increase of size, for the volume of the entire mass, deposited in the space of from twenty-four to thirtysix hours, almost always exceeds that of the animal even with its shell included. And the external envelope or shell acquires also additional opacity and hardness, which proceeds from the gradual and successive deposition of a great quantity of particles of carbonate of lime over its whole inner * Ann. des Sc. Nat. xxiv. p. 25, 37.

See also Encyclop. Method. i. 319. Lister has figured the egg. Hist. Conch. tab. 23, fig. 21.-The egg of Voluta brasiliana has a diameter of seventy millim. while the animal itself has only two hundred.-Ray Rep. on Zoology, &c. 1845, p. 119.

L. Reeve in Ann. and Mag. N. Hist. ser. 2, i. 273.-"The tropical Bulimi cement leaves of trees together to form an artificial nest for their large eggs."-OWEN's Lectures, 308.

surface. These particles, in the genus Helix, have the form of regular rhomboidal crystals, which we know is the primitive form of the crystals of carbonate of lime. The crystals are so large and fine that they may be made exquisite objects for the microscope, and we are, whilst viewing them, wrapped in admiration to conjecture by what subtle process of excretion and chemical affinity the fluid from which they are deposited must have been exhaled and left in a quietness not to disturb the regularity of the deposition on the first minute nucleus. The eggs of all the testaceous (terrestrial) Mollusca, according to M. Turpin, have the exterior envelope hardened in this manner, viz. by the addition of carbonate of lime on its internal surface, but very few of them offers the lime in the state of crystallisation exhibited in the egg of the Helices; but, on the contrary, it is, as in the eggs of birds, and in the bone of vertebrate animals, deposited in grains and confusedly. Such is the inference Turpin draws from an analysis of the ova of the Bulimus hæmastomus and Achatina variegata, among the largest of any Mollusks. The eggs of all the naked snails (Limacidæ) are soft, transparent, and entirely destitute of the calcareous particles or crystals; and it is curious to remark that the eggs of a genus which is intermediate between the shelled and naked tribes, the Cryptella of the Canary Isles, have the same neutral character, for the coat or shell is indeed covered interiorly with numerous crystals, but the crystals are ill-formed, and exhibit the rhomboid figure very imperfectly.*

Buffon has said that all shelled Mollusca are oviparous. This is true, in a physiological sense, when applied even to the whole class; but there are many exceptions to the axiom if we take the word oviparous in its popular meaning as signifying animals which extrude their young from the body enclosed in an egg. The only classes which in this latter view are unexceptionably oviparous are the Cephalopods, the Pteropods, and Brachiopods. The progeny of the Tunicata are not born until they have passed into the larvated state; and I have instanced a few viviparous species amongst the Bivalves, and the dioecious phytophagous

* Turpin in Ann. des Sc. Nat. xxv. 426, and in Ann. des. Sc. Nat. vi. (1836) 14. Part. Botanique.-The egg of Limax rufus has a calcareous shell according to Laurent. Ann. des Sc. Nat. (1835), iv. 249.

+"Omne vivum ex ovo, peut-on dire aujourd'hui avec plus de raison que dans les siècles précédents. Il n'y a plus un animal dont on ne connaisse ou l'appareil sexuel ou quelque moyen de reproduction."-VAN BENEDEN, Ann. des Sc. Nat. (1849) xi. 13.

BB

Mollusca. We find also a viviparous species where we should little expect, à priori, to find it, amongst the zoophagous Mollusks that produce concamerated nidi. The Yet (Fig. 29, p. 169), or Cymba neptuni is so; and the shell of the new-born young is an inch long. Adanson found four or five of these in one parent; and he thinks that the mother nurses them in the first months of their infancy, for he had seen several which carried about their five little ones in the folds of the elephantine foot until the shell of them had reached the length of an inch and a half.* The fragile species of Bulimi, with a simple lip to the shell, are mostly viviparous; the Partula, a genus allied to Vertigo, is similarly conditioned; and we find other viviparous hermaphroditical species in the genus Helix itself.

Adanson's anecdote of his "Yet" reminds me of some other species which make seemingly an amiable exception to that cold indifference to their ova and young which characterizes the vast majority of the Mollusca. The ancient naturalists indulge in stories of the Cuttlefish hatching their eggs and guarding their nests with jealous care; and, according to Aristotle, the female is often to be seen resting against the ground and covering the eggs with her body. The Ocythoë or Argonaut nurtures her eggs in her beautiful shell. Neritina fluviatilis is said to carry its offspring about on its shell; and the N. pulligera has got its name from a similar habit; but the inferences are probably deduced from some accidental occurrence or from misinterpreted observation, §-as has undoubtedly been done in the case of our common Limpet, when it was found, perchance, seated upon some very little individuals of its own species,-oppressing and not brooding on them. The Calyptraea affords a less exceptionable example, for this Gasteropod appears

* Senegal, 48.

"Mr. Adams regards the Argonaut shell as a nest formed by the female to contain her eggs; if this is correct, it can scarcely be compared to other shells. He regards the shell as similar to the cartilaginous cases which Murices and other zoophagous Mollusca form to contain their eggs; but it has no apparent analogy to those bodies, which are secreted by the oviduct as the eggs are deposited."-J. E. GRAY, Moll. Brit. Mus. 29. Edwards' Eocene Mollusca, 7.

Blumenbach's Nat. Hist. 265.

See also

"Grana, quæ dorsum cochleæ frequenter occupant, esse ipsius Neritæ pullos, Rumphius docet; horum ducenta triginta quinque in uno specimine numeravi, ovalia, convexa, extus luteo-albida, intus alba, moleculis referta, corpuscula hæc sæpe absterguntur, remanente in testa circulo ovali albo. Nisi obstaret autoritas exactissimi Rumphii, ovula peregrini animalculi putarem."-MÜLLER, Verm. Terr. et Fluv. ii. 196.

literally to sit upon and hatch its eggs. The mother disposes them under her belly, and preserves them, as it were imprisoned, between the foot and the foreign body to which she adheres, her patelloid shell thus serving not only to cover and protect herself, but as a shield to her offspring. The young Calyptraeæ are developed under this kind of maternal roof, and do not quit it until they have strength to attach themselves to the rock, and until their own shell is hard enough to afford protection when so attached. The eggs themselves are ovular corpuscules enclosed, like the zoophagous Mollusks, in membranous elliptical flattened capsules filled with an albuminous matter. The number of capsules varies from six to ten, each enclosing from eight to twelve eggs; and they are all joined together by a pedicle in such a manner as to make up the representation of a sort of cockade.*

Until very recently nothing was deemed, amongst malacologists, more certain than the axiom that no species in the sub-kingdom Mollusca was subject to a metamorphosis,but now the vivid language of some naturalists might lead you to suppose that they do all of them exhibit, in their progress from quickening to maturity, metamorphoses as striking and marked as those which insects offer to our study. This, however, is not exactly the case. It is admitted that the Mollusca have, indeed, in their embryo condition, or at birth, an appearance and a form very dissimilar to what they have in adolescence and adult age, and hence they may justly be said to metamorphose; but in their developement there are no stages-no arrests of growth, as in insects, but a gradual and imperceptible advance of transformation, which is completed in the very earliest days of life, and before the body has outgrown an almost microscopical minuteness.† "Semper ad eventum festinat."

The discovery of a metamorphosis in the class was first made, I believe, by M. Sars, a distinguished Norwegian naturalist, who has therefore the merit of having inserted the lever, which was to overturn and erase the long unquestioned error. The discovery was made on a species of the order Nudibranches; and it was soon shown to be general in this order by Alder and Hancock, Nordmann, Quatrefages, Löven, Peach,§ and Allman. Van Beneden earlier verified

Audouin and M. Edwards, Hist. Litt. de la France, i. 133. +M. A. de Quatrefages has, in an essay just published, pointed out this Embryogénie des Tarets" in Ann. des Sc. Nat. (1849) xi. Ray Reports on Zoology, 1847, p. 430. § Ann. and Mag. N. Hist. xv. 445.

distinction. 66 226.