The foundations of zoölogy / by William Keith Brooks.

Date:
1899
Catalogue details

Licence: Public Domain Mark

Credit: The foundations of zoölogy / by William Keith Brooks. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    know. Life is that which, when joined to mind, is knowledge,— knowledge in use; and we may be sure that all living things with minds like ours are conscious of some part of the order of nature, for the response in which life consists is response to this order. The statement that physical phenomena are natural seems to mean little, but the phenomena of life are so wonderful that many hesitate, even at the present day, to believe that nature can be such a wonderful thing as it must be if the actions of all living things are natural; and, as I shall try to find out in this course of lectures what we mean by the assertion that living nature is natural, I shall now attempt, by a few illustrations, to give a broad outline of some of the most nota- ble features of the nature of living things. The outer surface or shell of a crab is an excretion that is formed once for all; for while it may stretch a little at the joints, it does not grow, and as the living body must in time become too large for it, new shells, one size larger, are formed from time to time under the old one, which is then thrown off. The frequency of these moultings conforms to the rate of growth. The little crab sheds its shell either before or a few minutes after it is hatched from the egg, and a second moulting takes place within forty-eight hours, but the next interval lasts four or five days, and each successive shell remains useful for a longer time, until a mature crab may pass a year or even longer with- out moulting. The process is natural or mechanical, for nothing the crab can do for itself retards or hastens its growth or the secretion of a new shell; nor can any part of the process be attributed to its own actions, except so far as these actions are due to its nature, although it will not grow unless it seeks and finds food, nor will the old shell take itself off, unless the crab draws its limbs out by bodily movements which are both complex and violent. Many enemies, man and the hard crab among them, prize the soft crab as a palatable delicacy, and as it is helpless and defenceless while moulting, and until the new shell has grown hard, the crab hides under the sand or among the grass of the marshes until the dangerous crisis is past. No one can say whether the crab is or is not conscious of its danger, or whether it hides voluntarily or involun- tarily, but as no crab which has not escaped its enemies at the moult- ing season now survives, all the modern edible crabs hide by nature, just as they grow and shed their shells by nature. Some crabs pass