182 THE HAEMONIES OF NATURE. 



be indebted to this invaluable privilege, which frequently enables 

 them to save the whole by the temporary sacrifice of a part. 

 Here also the wind is tempered to the shorn lamb ! 



The wonderful metamorphoses of the insects are universally 

 known, but the changes which the young crabs, lobsters, prawns, 

 and shrimps have to undergo, before they assume their definitive 

 shape, are no less astonishing ; for the forms of these larvaB are so 

 peculiar, and so entirely different from any of those into which 

 they are ultimately to be developed, that they were considered 

 as belonging to a distinct genus, Zoea, until their real nature 



was first ascertained by Mr. T. V. 

 Thompson. These infant crabs look 

 very strange indeed. Fancy a prepos- 

 terously large helmet-shaped head, 

 ending behind in a long point, and 

 furnished in front with two monstrous 

 sessile eyes' like the windows of a lan- 

 tern. By means of a long articulated 

 tail, the restless chimera continually 

 Larva of dab. turns head over heels. Claws are 



wanting, and while the old crabs crawl about on eight legs, the 

 young have only four, armed at the extremity with four long- 

 bristles, that are continually pushing food towards the ciliated 

 and ever-active mouth. Who could imagine that a creature 

 like this should ever change into a crab, to which it has not the 

 least resemblance ? But time does wonders. After the first 

 change of skin, the body assumes something like its perma- 

 nent shape, the eyes become stalked, the claws are developed, 

 and the. legs resemble those of the crab ; but the change is 

 incomplete, for the tail is .still longhand furnished with false' 

 feet, like that of a lobster. The swimming-habit has not yet 

 been laid aside. At the next stage, while the little creature is 

 still about the eighth of an inch in diameter, the crab-form is 

 completed, the abdomen folding in under the carapace. All 

 the subsequent changes are merely changes of coat, consequent 

 on the growth of the now complete animal. 



In these several metamorphoses we see portrayed in succes- 

 sion the peculiarities of three different types, one rising above 

 the other in structure. In the first the crab is like one of the 

 lowest and most incomplete crustaceans ; further on it resembles 



