"The Salpæ, those strange gelatinous animals, through masses of which the voyager in the great ocean sometimes sails day after day, have been the subject of a great controversy since the time of the publication of the celebrated work of Chamisso, _De Animalibus Quibusdam e Classe Vermium Linnæana_. In this work there were set forth, for the first time, the singular phenomena presented by the reproductive processes of these animals,--phenomena so strange, and so utterly unlike anything then known to occur in the whole province of zoölogy, that Chamisso's admirably clear and truthful account was received with almost as much distrust as if he had announced the existence of a veritable Peter Schlemihl." According to Chamisso, salps appeared in two forms: solitary forms, and forms in which a number of salps are united into a long chain. Each salp of the aggregate form contains within it an embryo receiving nutrition from the mother by a connection similar to the placenta by which the embryo of a mammal receives nourishment from the blood of the mother. These embryos grow up into the solitary form, and the solitary form gives rise to a long chain of the aggregate form which developes in the interior of the body. Chamisso compared this progress to the development of insects. "Supposing," he said, "caterpillars did not bodily change into butterflies, but by a process of sexual breeding produced young which grew into the ordinary adults, and that these adults, as indeed they do, gave rise to caterpillars by sexual reproduction, then there would be a true alternation of generations." The first generation would give rise to a second generation totally unlike itself, and this second generation would reproduce, not its kind, but the first generation; such an alternation of generations he stated to occur among the salps. Huxley had an excellent opportunity to study this question at Cape York in November, 1849. "For a time the sea was absolutely crowded with Salpæ, in all stages of growth, and of size very convenient for examination." He was able to verify the general truth of Chamisso's statement. The aggregate form of Salpa always gives rise to the solitary salps, and the solitary salps always give rise to chains of the aggregate salps. But the process of reproduction he shewed to be quite different in the two cases. The solitary salp produces in its interior a little stolon or diverticulum which contains an outgrowth from the circulatory system, and this stolon gradually becomes pinched off into the members of the chain of the aggregate form. The salps of the aggregate form are therefore merely buds from the solitary form, and are not produced in the ordinary way, by sexual generation. On the other hand, each salp of the chain has within it a true egg-cell. This is fertilised by a male cell, and within the body of the parent, nourished by the blood of the parent, grows up into the solitary form.