110 ESSENTIALS OF ZOOLOGY 



vestiges and finally disappear when the young Nephrops 

 begins its life on the bottom. During the larval period of 

 weeks it is planktonic and drifts in the currents of the sea. 

 It moults three times and the abdominal limbs are produced. 

 The stages are similar to those of the lobster, Homarus. 



The period at which the larva is liberated varies some- 

 times even in the same order of Crustacea. In the primitive 



FIG. 53. Carcinus. The attachment of the eggs to the setae of the 

 pleopods. After Williamson. 



fresh-water groups, as in some of the others, the larva possesses 

 only the first three pairs of limbs, the two pairs of antennae, 

 and the pair of mandibles. This is called the nauplius larva. 

 The remaining limbs are added at successive ecdyses. Four 

 kinds of larvae are commonly found, and according to the 

 number of functional appendages these may be defined as: 

 three appendages, ' nauplius ' ; more than three but not more 

 than eight, * protozoea ' ; eight but not more than thirteen, 

 ' zoea ' ; all limbs present but not yet as adult, * megalopa.' 1 



1 Report Cullercoats Laboratory, 1918. 



