148 



THE LIFE OF CRUSTACEA 



may also serve in some cases as a protection 

 against enemies. The spines have been already 

 alluded to in describing the various larvae, but it may 

 be noted here that they are most strongly developed 

 in larvae which live in the open ocean ; for example, 

 the most elaborately armed of all Decapod larvae are 

 the zoea stages of Sergestes (Fig. 50), which, like the 



FIG. 52 Calocalanus pavo, ONE OF THE FREE-SWIMMING COPEPODA 

 OF THE PLANKTON. ENLARGED. (From Lankester's "Treatise on 

 Zoology," after Giesbrecht.) 



adults, belong to the oceanic plankton. The nau- 

 plius larvae of Cirripedes are all more or less spiny, 

 and the spines reach an exaggerated development in 

 the larvae of the genus Lepas (Fig. 51), of which the 

 adults are attached to floating drift-wood or the like, 

 and belong to the oceanic fauna, although hardly to 

 be classed with the plankton. 



