418 INVERTEBRATE MOBPHOLOOT. 



antennules are uniramous and, like the other limbs, but indis- 

 tinctly jointed, the antennules and mandibles being, however, 

 biramous and possessing strong setse at their bases which 

 function as jaws, though both pairs of appendages are essen- 

 tially locomotor. Judging from the appendages, therefore, the 

 Nauplius may be regarded as consisting of five segments, one 

 corresponding to the prostomial lobe of Annelids and contain- 

 ing the primitive cerebral ganglion (archicerebrum), one cor- 



FiG. 191. — NAiTPLrDB OF OetocliUus sepientrionalis (after Gbobbkn). 



responding to each pair of appendages and one to the region 

 of the body behind the mandibles. 



A Nauplius of this simple form may be regarded as typical 

 and is that which is found in the majority of the Copepoda and 

 in the Cirrhipedia as well as in some Branchiopoda [^stheria, 

 Limnadia). In the Ostracoda the arrangement of the limbs 

 and segments is the same, but the bivalved shell characteristic 

 of the adult is already developed, giving the Nauplius an ap- 

 pearance very different from that of the Copepoda. Not un- 

 frequently, however, as for instance in Apvs among the 

 Branchiopoda, and Leptodora among the Cladocera (the re- 

 maining Cladocera, so far as is known, leave the egg with the 

 adult form), the Nauplius, though possessing only the three 

 pairs of appendages, yet shows indications in the post-mandib- 

 ular region of a varying member of additional segments, and 

 to this form it is convenient to apply the name Metanauplius. 



As a rule in the Eutomostraca further development con- 

 sists of a series of moults (ecdyses), an increase in the number 

 of segments and appendages and modifications of the latter 

 taking place at each ecdysis, until the adult form is attained. 

 No special larval forms beyond the Nauplius are common to 



