THE CYCLE OF LIFE 



449 



fasts, living on its stores. Out of the egg of the Balanus 

 a nauplius larva Hkewise emerges. It feeds and grows 

 and moults, and acquires a firmer dorsal shield, a longer 



Fio. 71. — ^I. An acorn-shell (Balanus), showing : 1, the external rampart 

 of calcareous jiates ; 2, the valves which shut in over the retracted 

 body; 3, some of the thoracic appendages protruded. II. 

 The free-swimming larva of the same, known as a naupUus : 1, 2, 3, 

 first three pairs of hmbs, corresponding to the antennules, antennae, 

 and mandibles of the adult. It is almost microscopic. 



spined tail, and stronger appendages. It then changes 

 into a somewhat ' water-flea '-hke form — ^the Cyprid 

 stage — ^with two lateral eyes, six pairs of swimming append- 

 ages, a bivalve shell, and so on. It is very active, but it 



GG 



