134 BY THE DEEP SEA. 



its skin and became at once a Meg<ilopa. This was sufficiently 

 startling, when the best authorities had agreed that the 

 Crustacea went through no metamorpho'ses whatever ; but con- 

 tinuing to watch and observe, Megalopa was found at its next 

 moult to assume an undoubted crab-shape, and its progress 

 thereafter revealed what has ever since remained one of the 

 most important facts of crustaceology, that no such species as 

 Zoca and Megalopa exist, but that these forms are mere stages 

 in the development of a crab. 



As the crab grows and gets too large for its shell, the diffi- 

 culty of stretching or otherwise increasing the capacity of such 

 a strong-box arises. It cannot be met as in the case of 

 mollusks, by the simple but sufficient method of increasing the 

 length and breadth of the shell by adding new shelly matter to 

 the edge ; because the principal part of the crab's internal 

 machinery is in that part of his shell that has no proper edge. 

 .There is no help for it he must do as man does when his 

 .garments get too small to accommodate his growing body 

 and lengthening limbs : he gets a new suit. But a glance at 

 his armour-plated condition would suggest that the most diffi- 

 cult part of the business would be, how to get out of the old 

 suit ! It might not be such a hopeless task if his limbs were 

 straight and of equal thickness throughout ; but in every case 

 the joints are very much narrower than the rest of the limb. 

 Yet, in spite of this difficulty, by the shrinking of the body and 

 its limbs, and by the dissolution of partnership between the 

 upper and lower crusts, the crab, clad in a kind of parchment 

 suit, comes clean out, and leaves his old clothes intact, even to 

 the coverings of the eyes, the antennae, and the old jaws and 

 mouth-fittings. When the crab emerges from his old home, he 

 is, strange to say, much bigger than that empty presentment 

 of himself, and you might as well attempt to put back the 

 chick into the eggshell it has just vacated as to squeeze the 

 soft crab into his old husk. 



Very probably my reader will be so fortunate in some of 



