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Page:Popular Science Monthly Volume 38.djvu/270

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to his-well-matured principles, Chamisso contested in a special memoir.[1]

As a reward for his earnest exertions, and also as a warning against too narrowly limiting the circle of possibilities in organic nature, Chamisso himself was destined to make one of the most remarkable discoveries in the region of metamorphism. This was in the case of the Salpæ, those soft, transparent organisms which, clinging to one another, swim over the sea in chains of from twenty to forty members. Besides the chains there are individual salpæ, but of two kinds, one of which bear traces in their organs of adherence of having been members of a chain, while the others do not. During a calm, on the voyage from Plymouth to Teneriffe, Chamisso made the surprising observation that the individual salpæ which have never belonged to a chain bear a progeny resembling the chain salpæ; while he found in the members of a chain young of forms agreeing with those of the single salpa. The salpæ of the chain, which produce single salpæ, are hermaphrodite; the single salpæ are asexual, and the chains are developed in them without fertilization, by inner budding. They thus alternate every two generations, one of which is sexual, and the other asexual and propagating itself by budding; and they are distinguished by other marks. To use Chamisso's figure, a salpa does not resemble its mother or its daughter, but its grandmother, its sisters, and its aunts. Chamisso called this kind of propagation that by alternating generations. So new and unprecedented was this discovery that, although Chamisso related it after his return in 1819, in a special Latin publication,[2] it either passed unheeded, or was stamped upon. But there came to Copenhagen, in 1842, a defender and champion of Chamisso's fame in J. Steenstrup, who discovered that the process of propagation by alternating generations such as Chamisso described was common to a series of organisms, including the Medusæ, and Strobilæ, the Cercariæ and Distomæ, and the aphides or plant-lice, to which many others have since been added; so that the whole matter was cleared up in a trice. Johannes Müller's famous discoveries concerning the development of the echinoderms furnish a transition between the phenomena of alternation and those of metamorphosis as illustrated in the frogs and butterflies. The honor of having led the way to these discoveries belongs, as Steenstrup has expressly declared, to the accurate and ingenious investigator Chamisso.[3]

  1. Ein Zweifel und Zwei Algen (One Doubt and Two Sea-weeds), 1829.
  2. De animalibus quibusdam c classe vermium Linnæana in circumnavigatione terræ... observatis, etc. (On Certain Animals of the Linnæan Class of Worms observed in the Circumnavigation of the Earth.) Fasc. 1, De Salpa. Berlin, 1819.
  3. Steenstrup on Alternating Generations. Copenhagen, 1842.