4 THE FOUNDATIONS OF ZOOLOGY 



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 ^gg^ 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 



