that, in drying, the secretion assumes the beautiful deep hue of the sweet scabious (Scabiosa atro-purpurea, Linn.), and remains unaltered by long exposure to the air. Nitric acid, in small quantity, heightened the tint, but a larger dose changed it to a dirty aurora; and potash changed it to a dirty vinous grey colour: both the acid and alkali precipitated many white flakes from the fluid. The smell is faint: there is nothing peculiar in the taste; nor has it any irritating quality, for it may be applied a long time to the skin with perfect impunity.* The liquid of our native species is a beautiful purple when exuded. In dyeing it becomes of a brown colour; and if a tincture is made by macerating the Aplysia in whiskey, the purple colour is retained for some time, but ultimately the tincture assumes a tint much like port-wine. The excretion which approaches apparently nearest to this in its character is that of the Ianthina; but I am not aware that any analysis has been made of it. Planorbis corneus (Fig. 42), also, when irritated by any means, or, as Fig. 42. Wallis translates a passage from Lister, by "an injection of a grain of salt, pepper, or ginger, into its mouth," pours forth a purple fluid from the sides, between the fork and margin of the cloak; but the colour is of so fugitive a nature, that no acid or astringent has hitherto been found sufficient to preserve the elegancy of its tint, and from turning to an unpleasant rusty hue. In this respect it agrees with the liquor discharged by Scalaria clathrus, of which Montagu has given us an interesting history. "The purple juice," he tells us, may be collected either from the recent or dried animal, by opening the part behind the head; and as much can be procured from five individuals as is sufficient, when mixed with a few drops of spring-water, to cover half a sheet of paper." ." Neither volatile nor fixed alkali materially affects it; mineral acids turn it to a bluish green, or sea-green; sulphuric acid renders it a shade more inclining to blue; vegetable acids probably do not affect it, since cream of tartar did not in the least alter it. These colours, laid on paper, were very bright, and appeared for some months unchanged by the action of the air or the sun; but, being exposed, for a whole summer, to the solar rays, in a south window, they 66 * Mém. ix. 7. + Wallis, Nat. Hist. North., i. 371. Lister, in his Anim. Ang. 144, gives a full and very good account of this liquor. almost vanished. The application of alkali to the acidulated colour always restored it to its primitive state, and it was as readily changed again by mineral acid: in this particular it differs materially from the succus of Buccinum lapillus, which, as we have before remarked, is unalterable."* It is from the difference pointed out, in the latter part of the sentence just quoted, between the fluid of Scalaria (and, I may add, of Ianthina and Aplysia) and the Buccinum or Purpuriferæ, and because it is from the first of a purple colour, that I cannot agree with Plancus,† Colonel Montagu, and many other naturalists of eminence, in their opinion, of its having formed any part of the Tyrian dye; for unchangeableness was one of the characters that enhanced the value of the latter; and Aristotle and Pliny state expressly that the colour of that fluid, on its first discharge from the animal, was white. Such a coloured liquor can be procured, as these authors say it was procured, from several univalves belonging to the genera Murex and Purpura; ‡ and Colonel Montagu furnishes us with a good account of it in the Purpura lapillus :-"The part containing the colouring matter is a slender longitudinal vein, just under the skin on the back, behind the head, appearing whiter than the rest of the animal. The fluid itself is of the colour and consistence of thick cream. As soon as it is exposed to the air, it becomes of a bright yellow, speedily turns to a pale green, and continues to change imperceptibly, until it assumes a bluish cast, and then a purplish red. Without the influence of the solar rays, it will go through all these changes in the course of two or three hours; but the process is much accelerated by exposure to the sun. A portion of the fluid, mixed with diluted vitriolic acid, did not at first appear to have been sensibly affected; but, by more intimately mixing it in the sun, it became of a pale purple, or purplish red, without any of the intermediate changes. Several marks were now made on fine calico, in order to try if it was possible to discharge the colour by such chemical means as were at hand; and it was found that, after the colour was fixed at its last natural change, nitrous no more than vitriolic acid had any other effect than that of rather brightening it: aqua regia, with or without solution of tin, and marine acid, produced no change; nor had fixed or volatile alkali any sensible effect. It does not in the least give out its colour Test. Brit. Supp. 122. + De Conchis minus notis, 28. Of Tritonium nodiferum Philippi says, "Animal in siccum positum paullo ante mortem saniem pulcherrime cœlestem exspuit."- Moll. Sicil. ii. 184. to alcohol, like cochineal and the succus of the animal of Turbo (Scalaria) clathrus; but it communicates its very disagreeable odour to it most copiously, so that opening the bottle has been more powerful in its effects on the olfactory nerves than the effluvia of assafoetida, to which it may be compared. All the markings which had been alkalised and acidulated, together with those to which nothing had been applied, became, after washing in soap and water, of a uniform colour, rather brighter than before, and were fixed at a fine unchangeable crimson."* The fluid excreted by some of these mollusks is of a green colour. When the snail of the Purpura patula is retracted within its shell, if you press on the operculum, a very considerable quantity of a greenish liquor is shed, but it becomes a deep purple in drying; and Adanson is a good authority for saying that the greater number of the species discharge a similar tincture. The colour of it appears, however, to be more permanent in the species of Cerithium,-a genus not much removed in nature from Purpura. Two specimens of Cerithium armatum were brought alive to London from the Mauritius, kept, during their long voyage, not in sea-water, as you might imagine, seeing that the animal is aquatic, but in a dry state, and affording a remarkable illustration of the tenaciousness of its life. The animal was apparently healthy and beautifully coloured: it emitted a considerable quantity of bright green fluid, which stained paper of a grass-green colour; it also coloured two or three ounces of pure water. This green solution, after standing for twelve hours in a stoppered bottle, became purplish at the upper part; but the paper retained its green colour though exposed to the atmosphere. A tincture made by immersing the animal of Cerithium telescopium in spirits, became of a dark verdigris colour, which it retained for some weeks.§ 6. URINARY SECRETIONS. Blainville seems to be of opinion that the coloured secretions now noticed are analogous to the urinary secretion of vertebrated animals; || but although the opinion has been adopted by many authors,¶ yet of its correctness doubts may be reasonably entertained. Besides their purple fluid, the Aplysiæ occasionally discharge, but in small quantities, a whitish acrid one, secreted by a gland composed of little round hyaline grains, and Test. Brit. Supp. 106. Proc. Zool. Soc. iii. part ii. 22. || Manuel, p. 160. p. 220. + Senegal, Coquil. i. 106. Raspail's Organic Chemistry, p. 529; Tiedemann's Comp. Physiology, emitted by a circular hole that opens externally a little behind the aperture of the oviduct.* The Doris ejects a similar milky fluid, which, however, comes from the liver, or from a gland so intimately associated with it as not to be separated by any dissection. The position of this secretory organ is singularly modified in the family Eolidæ, where it is found within the apices of their dorsal papillæ, distributed in correspondency with the disintegrated condition of the liver. The organ, first discovered by Messrs. Alder and Hancock, is "a small ovate vesicle, which communicates with the biliary gland by means of a slender canal below, and at the opposite and narrower end opens externally through a minute aperture at the extreme apex of the papilla." It is filled with elliptical bodies and globules of various sizes, imbedded in a mucus-like water; and these contents are, from time to time, expelled as it were by a convulsive contraction of the vesicle. Immediately on expulsion into the circumfluent water, the elliptical bodies burst the little bags in which they are packed in parcels, and shoot out each a long hair-like tail, as they are being scattered abroad. On one occasion our distinguished friends "observed an individual of Eolis picta, when moving freely about, suddenly, and by a convulsive effort, eject from the points of the papillæ a minute stream of milk-white fluid, which curling upwards, mingled with the surrounding liquid, and was soon lost to view. The fluid exactly resembled the contents of the ovate vesicle when forced out by pressure, and examined with a lens of low power." + In some univalved mollusca, a urinary discharge has been more positively ascertained. Swammerdam detected in the snail a little oblong triangular part, placed near the heart, which he calls the "sacculus calcareus." This organ has a pretty large duct, which runs into the intestine; and Swammerdam believes it to be a gland whereby the calcareous matter of the blood is drained from the body, and deposited in the intestine; "and accordingly we find that such a matter is sometimes mixed with the excrements."§ The organ is found, in a modified shape, in many other mollusca ; and some naturalists || have imagined that the shell was * Cuvier, Mém. ix. 24. + Cuvier, Mém. v. 16. Monog. Nudib. Moll. part iii. pl. 7 and 8; Ann. and Mag. N. Hist. xv. 82; Nordmann in Ann, des Sc. Nat. (1846), v. 124. § Book of Nature, 49. "The formation of the calcareous matter of their shells, which takes place in a peculiar viscus lying near the heart (sacculus calcareus, Swamm. glandula testacea, Poli").-BLUMENBACH'S Man. Comp. Anat. 251, transl. formed by it, misled apparently by the name given by Swammerdam; for no opinion was ever more groundless or hastily offered. Cuvier considers it as the source of the mucus which snails excrete so profusely when forced to withdraw suddenly into their shells, and with which they fix their shells to smooth bodies:* but Mr. Jacobson has proved that it performs the functions of a kidney. "Chemical analysis of the matter secreted by this organ, has led him to discover in it uric acid, ammonia or calcareous salt, and water. His experiments were made on the great snail (Helix pomatia). He was unable to discover any trace of uric acid in any other part of the animal. And as, in the superior animals, the kidneys are the only organs which, in a state of health, secrete uric acid; and as the calcareous sac of the snails has many other anatomical relations with the kidneys, Mr. Jacobson concludes that this sac represents the kidneys, and must be so considered in all the mollusca which are provided with it."† 7. Mucus. All molluscous animals excrete a mucous fluid to lubricate the skin, furnished by the skin itself, or by some crypts situated in it. This mucus is, in general, possessed of no remarkable properties: it is usually colourless, but in some species milky or yellow, as you are aware is exampled among our native slugs; and the Clios, a genus of marine pteropods, envelope themselves, when in danger, with a whitish cloudiness that appears to exude from the whole surface of the body. The smell also which certain mollusks exhale, is probably a principle of this mucus. The Octopus moschatus is distinguished for the "amber scent of odorous perfume," which that cuttle exhales so strongly as to fill quickly a whole apartment, whether the animal be dead or alive, and whence it derives its specific designation.‡ I have already told you that the Aplysia of southern Europe stinks disagreeably; but, according to Rapp, the Tethys entices us not more by its singular beauty, than by its odour, which he compares to that of roses. Rondeletius might doubtless be quoted for a very opposite virtue in Tethys,§ but not by an advocate of the tribe. Helix pomatia smells strong of hemlock, in the beginning of June, a smell which * Mem. xi. 26. + Edinb. Journ. Nat. and Geogr. Science, iii. 325. Bosc maintains that ambergris derives its scent from this cuttle, on which the whale feeds.-Hist. Nat. des Vers, i. 48. "Odore est valde ingrato et pisculento, nauseam movet, splendore diutius inspectantibus dolorem oculorum capitisque adfert, id quod in meipso sum expertus."-RONDEL. de Pisc. 527. |