‘marks. It may be ‘described, 
ENTOMOSTRACA. 305 
moulted, though disintegrated portions may be removed in flakes and 
renewed by fresh formations. 
In the allied genus Scalpellum, 
some are like Lepas, hermaph- 
rodites, without complementary 
males (Sc. dalanozdes); others 
are hermaphrodite, with comple- 
mentary males (Sc. v2llosum) ; 
and others are unisexual, but 
the males are minute and para- 
sitic (Sc. regezm). 
Balanus, the acorn-shell, en- 
crusts the rocks in great numbers 
between high and low water 
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 Leas, by 
a fold of skin, which forms a 
rampart of six or more cal- 
careous plates, and a fourfold 
lid, consisting of two scu¢a and 
two ¢erga. 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 Cyprds 
stage, with two side eyes, six 
pairs of swimming legs, a bi- 
valve shell, and other organs. 
Fic. 159.—Development of Saccudina. 
As it exerts itself much but does ae Delage. (Not drawn to 
not feed, it is notunnatural that °° €.) 
it sHould sink down as if in 4., Sereswimnting Tapplius, with tees 
: . . pairs of appendages ; B., pupa stage; C., 
ek d re ees gout protruding from the abdomen of a 
? crab. 
by the secretion of the cement 
gland. Some of the structures, ¢.g, the bivalve-shell, are lost; new 
20 
