ACORN SHELLS 91 



days old, but spend their whole lives fastened 

 down to the surface of the rocks. But there is 

 this great difference between the two. When 

 the eggs of a limpet hatch, out come a number 

 of very tiny limpets, just like their parent in 

 everything except size. But when the eggs of 

 an acorn shell hatch, the little creatures which 

 come out from them are not like their parents 

 at all. They are " zoeas," in fact, or acorn shell 

 caterpillars; and they do not reach their perfect 

 form for some little time. 



When these little "zoeas" first make their 

 appearance in the world they are able to swim 

 about by means of three pairs of tiny feathery 

 legs, with which they paddle their way along 

 through the water. And they also have a round 

 black eye in the middle of the body, with which 

 they can see quite well. Every two or three 

 days they throw off their skins, just as caterpillars 

 do, and appear in new ones, which have been 

 gradually forming beneath. And each time that 

 they do this their shape changes. At last 

 they are ready to take their perfect form. Then 

 each of the little creatures clings to the surface 

 of a rock by means of its feelers, and pours 

 out a kind of cement, which hardens round 

 them, and anchors it firmly down. It then 

 throws off its skin once more, and appears in 

 the form of an acorn shell just like its parent. 

 And, strange to say, it throws off its eye at 



