Upon animal individuality / Thomas H. Huxley.

  • Huxley, Thomas Henry, 1825-1895.
Date:
[1852]
Catalogue details

Licence: Public Domain Mark

Credit: Upon animal individuality / Thomas H. Huxley. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    Each of these carries a single ovum, from which the first form is again developed. The Salpa mucronata, which is thus produced from the Salpa de- mocratica, is just as highly organized as the latter. It has as com- plete a circulatory, nervous, and digestive apparatus, and moves about and feeds as actively ; no one unacquainted with its history would dream of its being other than a distinct individual animal, and for such it has hitherto passed. But the Salpa mucronata has exactly the same relation to the S. democratica that the free-medusiform egg-producing body of Physalia or Velella has to the Physalia or Velella ; and this free-medusiform body is homologous with the fixed medusiform body of Diphyes ; which again is homologous with the semi-medusiform, fixed body of a Tubularia and with the egg-producing process of the Hydra. Now as all these bodies are homologous with one another, one of two conclusions is possible ; either, considering the Salpa mucronata to be an individual, we are logically led to look upon the egg- producing process of Hydra as an individual also, which seems absurd. Or starting with the assumption that the egg-producing process of Hydra is a mere organ, we arrive at the conclusion that the Salpa mucronata is a mere organ also : which appears equally startling. The whole question appears to turn upon the meaning of the word “ individual.” This word the Lecturer endeavoured to shew always means, merely, “ a single thing of a given kind.” There are, however, several kinds of Individuality. Firstly, there is what may be called arbitrary individuality, which depends wholly upon our way of regarding a thing, and is therefore, merely temporary : such is the individuality of a landscape, or of a period of time ; a century for instance. Secondly, there is an individuality which depends upon something else than our will or caprice; this something is a fact or law of co- existence which cannot be materially altered without destroying the individuality in question. Thus a Crystal is an individual thing in virtue of its form, hard- ness, transparency, and other co-existent qualities; pound it into powder, destroy the co-existence of these qualities, and it loses its individuality. Thirdly, there is a kind of individuality which is constituted and defined by a fact or law of succession. Phenomena which occur in a definite cycle are considered as one in consequence of the law which connects them. As a simple instance we may take the individuality of the beat of a pendulum. An individual beat is the sum of the successive places of the bob of the pendulum as it passes, from a state of rest to a state of rest again. Such is the individuality of living, organized beings. Every or-