460 PHYLLOPODA. 



The free larval stages when such exist commence with a 

 larval form known as the Nauplius. 



The term Nauplius was applied by O. F. Muller to certain 

 larval forms of the Copepoda (fig. 229) in the belief that they 

 were adult. 



The term has now been extended to a very large number of 

 larvae which have certain definite characters in common. They 

 are provided (fig. 208 A) with three pairs of appendages, the 

 future two pairs of antennae and mandibles. The first pair of 

 antennae (an 1 ) is uniramous and mainly sensory in function, the 

 second pair of antennae (an*) and mandibles (md) are biramous 



A qn 



FlG. 208. TWO STAGES IN THE DEVELOPMENT OF APUS CANCRIFORM1S. 



(After Claus.) 



A. Nauplius stage at the time of hatching. 



B. Stage after first ecdysis. 



an 1 , and a 2 . First and second antennae ; md. mandible ; MX. maxilla ; /. labrum; 

 fr. frontal sense organ ; /. caudal fork ; s. segments. 



swimming appendages, and the mandibles are without the future 

 cutting blade. The Nauplius mandibles represent in fact the 

 palp. The two posterior appendages are both provided with 

 hook-like prominences on their basal joints, used in mastication. 

 The body in most cases is unsegmented, and bears anteriorly a 

 single median eye. There is a large upper lip, and an aliment- 

 ary canal formed of cesophagus, stomach and rectum. The anus 

 opens near the hind end of the body. On the dorsal surface 

 small folds of skin frequently represent the commencement of a 

 dorsal shield. One very striking peculiarity of the Nauplius 

 according to Claus and Dohrn is the fact that the second pair 

 of antennae is innervated from a sub-oesophageal ganglion. A 

 larval form with the above characters occurs with more or less 

 frequency in all the Crustacean groups. In most instances it 



