ENTOMOSTRA CA. 



305 



moulted, though disintegrated portions may be removed in flakes and 



renewed by fresh formations. 



In the allied genus Scalpelhtm^ 



some are like Lepas, hermaph- 



rodites, without complementary 



males (Sc. balanoides] ; others 



are hermaphrodite, with comple- 



mentary males (Sc. yillosum} ; 



and others are unisexual, but 



the males are minute and para- 



sitic (Sc. regium}. 



Balanus, the acorn-shell, en- 

 crusts the rocks in great numbers 

 between high and low water 

 marks. It may be described, 

 in Huxley's graphic words, as a 

 crustacean fixed by its head, 

 and kicking the food into its 

 mouth with its legs. The body 

 is surrounded, as in Lepas, by 

 a fold of skin, which forms a 

 rampart of six or more cal- 

 careous plates, and a fourfold 

 lid, consisting of two scuta and 

 two terga. When covered by 

 the tide, the animal protrudes 

 and retracts between the valves 

 of the shell six pairs of curl -like 

 thoracic legs. The structure 

 of the acorn-shell is in the main 

 like that of the barnacle, but 

 there is no stalk. 



The life history also is similar. 

 A Nauplius is hatched. It has 

 the usual three pairs of legs, an 

 unpaired eye, and a delicate 

 dorsal shield. It moults several 

 times, grows larger, and ac- 

 quires a firmer shield, a longer 

 spined tail, and stronger legs. 

 Then it passes into a Cypris 

 stage, with two side eyes, six 

 pairs of swimming legs, a bi- 

 Salve shell, and other organs. 



As it exerts itself much but does 



scale. ) 



T 

 FlG ' 



Delage. (Not 



not feed, it is not unnatural that 

 it should sink down as if in 

 fatigue. It fixes itself by its 

 head and antennae, and is glued 

 by the secretion of the cement 

 gland. Some of the structures, e.g. the bivalve shell, are lost ; new 



A., Free-swimming Nauplius, with three 

 pairs of appendages ; B., pupa stage ; C., 

 adult protruding from the abdomen of a 

 crab. 



