5 6 



THE CRUSTACEANS. 



As the shelly armor of the Crustaceans is, in most cases, so hard, strong, and 

 unyielding, the mode of growth might be considered a problem not very easy of so- 

 lution. For with the Crustaceans the growth continues during nearly the whole of 

 life, or at all events for several years after they have passed through the various changes 

 to which they are subjected in their imperfect stages of existence. Their increase of size 

 and weight is marvellously rapid, and how it can be accomplished without subjecting 

 the Crustaceans to the lot of the starveling mouse, who crawled into a jar of corn, but 

 could not crawl out again after feasting on its contents, seems to partake of the 

 character of an animated puzzle. 



The answer to the problem is simply that the creature sheds its armor annually, 

 expands rapidly while yet covered only by a soft skin, and is soon protected by a 

 freshly-deposited coat of shelly substance. Even this answer contains a second 



Steaorhyacbus Phalanglum. 

 Leptopodia sagittate. 



problem little less difficult than that which it solves. How can a Crustacean, say a 

 crab or a lobster, shed its skin ? It is true that the cast shells are found, showing 

 that the creature has escaped from its old and contracted tenement by a slit in some 

 part of the body, such as the top of the carapace, and has left its shell in so perfect a 

 state that it might easily be mistaken for the living animal. 



But how did it manage about the claws ? We all know what large muscular masses they 

 are, how very small is the aperture in which the joint works, and how stiff and firm is the 

 broad tendinous plate which is found in their interior. Examination shows that there is no 

 opening on the claws through which the creature might have drawn the imprisoned limb, 

 and it is also evident that the only method by which these members can be extricated, is 

 by pulling them fairly through the joints. As a preliminary step, the hard, firm, muscular 

 fibres which fill the claw and give it the well-known pinching power, become soft, flaccid 



