CRABS, ETC. 



8l 



of the abdomen (Fig. 85), and are carried about by the 

 mother. When first hatched they are generally in the 

 zoaea stage. The eyes of the zoaea (Fig. 

 87, a) are large and black. From the 

 carapace extends upward a long horn, an- 

 other projecting downward like a tusk. 

 They moult several times, gradually chang- 

 ing to the megalops form (Fig. 87, ), and 

 finally, after successive moults, seek the FlG - 86 -~ A few e ^ s 



. 1,1 /T-- from a common 



bottom and assume the adult shape (Fig. CTab enlarged. 

 87, c). (After Morse.) 



Order I. Barnacles (Cirripcda). The 

 barnacles are fixed crustaceans, and partly from this cir- 

 cumstance were long considered mollusks. The adult 



FIG. 87. Metamorphosis of the crab (Qzrctnus nuznas). A, zoaea stage ; 

 B, megalops stage ; C, ready to seek the bottom. 



Balanus (Fig. 88) is round, with a broad base, and at- 

 taches itself to shells or rocks. The newly hatched young 

 are free-swimmers (Fig. 89, A), but soon acquire a bivalve 

 shell, B, and attach themselves to the bottom by their 



