VIII 



ARTHROPODA 



201 



forked nature and swimming function of the second antenna, so that 

 in their case the "critical" character of the moult is reduced to the 

 loss of the distal joints of the mandible. 



The Cirripedia also begin their free life as Nauplius larvae, which 

 in all essentials, and even in such minute points as the many-jointed 

 exopodite and feebly-jointed endopodite, agree with the larvae of 

 Cyclops. They differ in the development of the dorsal integument 

 into a great triangular shield, with two antero- dorsal horns, the 

 dorso-lateral spines, and one postero-dorsal horn, the caudal spine, 



ter 



fix 



FIG. 148. The fixation of the "Cypris" larva of Lepasfascicularis. (After Willemoes-Siihm. ) 



A, the larva just in the act of ecdysis after fixation. B, the young Barnacle fixed to a piece of dead 

 shell. Letters as before. In addition, en, carina ; l.nar, valves of larval carapace ; Itli, larval thoracic 

 appendages being cast off; sc, scutum ; ter, tergum ; th, adult thoracic app. 



forming its three angles, and in the possession of a ventrally directed 

 pre-anal spine. Further, we find in front of the first pair of appen- 

 dages a pair of flexible antennae, the frontal filaments. As the 

 larva grows the thoracico- abdominal portion of the body becomes 

 divided into segments, on which six pairs of bilobed appendages are 

 successively developed, whilst in the angle between this rudiment 

 and the head the two pairs of maxillae appear as buds. Beneath the 

 edges of the dorsal shield the rudiments of the paired eyes appear 

 as dark areas. Then comes the critical moult, when the second pair 

 of appendages completely disappears, and the third is reduced to 



