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DIVERSIONS OF A NATURALIST 



It is not every one who has the chance of seeing 

 living ship's barnacles (Lepas), but anyone can pick up 

 a stone or bit of rock on the seashore with live sea-acorns 

 or acorn-barnacles (Balanus) adherent to it. Each is 

 like a little truncated volcano (Fig. ii), the sides of 

 which correspond to the pair of larger shells of the ship's 

 barnacle, fused together and grown into a cone-like wall. 

 The acorn-barnacle has no stalk, but adheres by its 

 broad base to the stone. Just within the shelly crater 

 are four small hinged plates or valves in pairs, identical 

 with the smaller shelly bits of the ship's 

 barnacle. When you first see your 

 specimen, the valves are tightly closed. 

 After a few minutes in a glass of sea- 

 water they open right and left, and up 

 jumps — ^jack-in-the-box- wise — a tuft of 

 bowing and scraping feelers or tentacles, 

 like those of the ship's barnacle. If 

 disturbed, they shoot inwards, and the 

 valves close on them like a spring trap- 

 door. 



Fig. II. — A large 

 British Sea-acorn, 

 Balanus porcatus, 

 allied to the Ship's 

 Barnacle. /, the 

 feather - like legs 

 issuing from the 

 shell. Drawn of 

 the natural size. 



Now, these clawing, feathery little 

 plumes are found, when we examine 

 them with a hand-glass, to be six pairs in number, and 

 each of them is Y-shaped, like the swimmerets of a 

 lobster. The arms of the Y are built up of many 

 little joints and covered with coarse hairs. As a result 

 of the study of the young condition of the ship's 

 barnacle and the sea-acorn, we find that these six pairs 

 of Y-shaped plumes are six pairs of legs corresponding 

 to those of the mid-body (some of the walking legs and 

 some of the foot-jaws) of the lobster, and that the shelly 

 hinged plates of the barnacles correspond to the over- 

 hanging sides of the " head '' of the lobster and prawn, 



