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Page:Popular Science Monthly Volume 35.djvu/339

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319
SEA-BUTTERFLIES.

their relatives could be seen laying eggs, with transparent shells, which resembled rosaries or long pods, in the spaces of which the eggs swam in a clear liquid. Do they lay these eggs because they are comfortable in the vessel, or in order to rid themselves of what is a burden in their straitened captivity? While this question is still unanswered, it is certain that such strings of eggs and pods are also found drifting in the open sea, that the eggs which are laid in captivity are usually fertilized, and that the development of the embryo can be followed under the microscope—at least, till the point when the larvæ, which go through many metamorphoses, leave the shells to swim in the sea. These do not resemble the parents, but the larvæ of creeping sea-mollusks, and swim by means of a ciliary apparatus which grows on the head, and afterward, when the wings have been formed, is repressed. The free larvæ have not been successfully raised any further in captivity. Probably they die of hunger, for it is impossible to feed them. But we can fish them out of the sea in a net, and can compare from the various forms found among them the succession of single steps in their growth to the adult state. This is, indeed, not always easy, for, on the one hand, the larvæ of different species are often very much alike, and, on the other hand, the currents do not always fetch what is wanted, so that many observers have to wait year after year to continue their observations and bring them to a conclusion.

Dealing with the pelagic animals that swim on the high sea is a delicate matter, and, despite the most careful researches, the

PSM V35 D339 Creseis acicula hyalea tridentata cleodora lanceolata.jpg
Fig. 3.—Creseis acicula. Fig. 4.—Hyalea tridentata. Fig. 5.—Cleodora lanceolata.

cause of their appearance and disappearance has never been ascertained. In the years from 1850 to 1852, which I spent in Nice, and when I fished with my fine net at least twice a week in the Bay of Villafranca, I only found a few species of needle-butterflies and related species. Cymbuliæ, which could not have escaped me then, I first found at a visit in the Easter vacation of 1867, when they were very numerous. Messina is the Mediterranean station