Animal life in the sea and on the land . Fig. 96.—, operculum; s, siphon. 4. What Forms the Spines on some Shells ?—The edgesand notches of the old rim are often marked upon theoutside of the shell, and there are sometimes long, bris-tling spines sticking out from them. How could thesespines have been formed ? Wherever there is a spine,there must have been at that point a fold of the mantlepushed out over the rim of the shell to form a fold, like every other part of the mantle, depositedshelly matter, and finally formed the stiff spine. Of 160 ANIMAL LIFE IN THE SEA AND ON THE
Animal life in the sea and on the land . Fig. 96.—, operculum; s, siphon. 4. What Forms the Spines on some Shells ?—The edgesand notches of the old rim are often marked upon theoutside of the shell, and there are sometimes long, bris-tling spines sticking out from them. How could thesespines have been formed ? Wherever there is a spine,there must have been at that point a fold of the mantlepushed out over the rim of the shell to form a fold, like every other part of the mantle, depositedshelly matter, and finally formed the stiff spine. Of 160 ANIMAL LIFE IN THE SEA AND ON THE course, it is of no further use after the rim has grownbeyond it. 5. Most of those gasteropods that have the margin ofthe shell notched and lengthened into a canal are flesh-eaters, whereas those having an entire and even marginlive on vegetable food. 6. Gasteropods Highly Organized. — Gasteropods, as ageneral thing, are quite highly organized. They have adistinct head, with two tentacles, and eyes that are some-times stalked; they are believed to have the senses of hearing and of taste, also, whichindicates a high-er stage of devel-opment than thatof the oyster andclam. 7. Siphon —Operculum.—Water is admit-ted within the body by means of a siphon, and at this pointthe shell is often lengthened into a long canal. The thicktough foot may be extended entirely beyond the shell, butgasteropods are timid creatures, and when alarmed allparts of the body are instantly drawn in, and the entranceis closed with a horny plate on the foot, which is repre-sented at o, Fig. 96. This plate fit
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1887
