A Goodly Company of Crabs 



their young ones up into higher levels for educa- 

 tion. There for a while the juveniles swim and 

 develop, till old enough in their turn to take to 

 the ocean-bed. Great numbers have meanwhile 

 been preyed upon by multitudes of fishes in those 

 upper levels. 



Crabs undergo curious changes in the course 

 of their growth from infancy to adult age. At 

 certain stages they are so utterly unlike in 

 appearance to what they become later, that for 

 a long while they were classed by naturalists 

 under separate names, being actually reckoned 

 as different creatures. 



Since the protecting armour of a crab is far 

 too rigid to admit of its stretching, it becomes 

 from time to time too tight for the growing body 

 within. When it can no longer be endured, it 

 has to be cast off, and a new suit, larger in size, 

 has to form in its place. 



This armour, like the shells of foraminifers, 

 and the skeletons of coral - polyps, is uncon- 

 sciously secreted by the crab ; and during the 

 formation of a new suit of armour the crab has 

 a time of weakness, of delicate health, and also 

 of dangerous exposure to the attacks of enemies. 



Some kinds of crabs have sunk to the miser- 

 able level of parasites, living on the exertions of 



Q 225 



