410 CIRRIPEDIA. 



not jointed, but in other Nauplii, e.g. that of Lepas fascicularis, 

 the jointing is well marked. In Lepas fascicularis the earliest free 

 Nauplius is enveloped in a larval skin, which is thrown off after a few 

 hours. The Nauplii of all the Thoracica undergo a considerable number 

 of moults before their appendages increase in number or segmentation 

 of the body appears. During these moults they grow larger, and the 

 posterior part of the body the future thoracic and abdominal region 

 gi-ows relatively in length. There also appear close to the sides of 

 the unpaired eye two conical bodies, which correspond with the 

 frontal sense organs of the Phyllopods. During their growth the 

 different larvae undergo changes varying greatly in degree. 



In Balanus the changes consist for the most part in the full seg- 

 mentation of the appendages and the growth and distinctness of the 



FIG. 231. NAUPLIUS LARVA OF LEPAS FASCICULARIS VIEWED FROM THE SIDE. 

 oc. eye; At. 1. antenna of first pair ; At. 2. antenna of second pair; md. mandible; 

 1b. labrnm; an. anus; me. mesenteron; d.sp. dorsal spine; c.sp. caudal spine; 

 Vp. ventral spine; Ih. lateral horns. 



dorsal shield, which forms a somewhat blunt triangular plate, broadest 

 in front, with the anterior horns very long, and two short posterior 

 spines. The tail also becomes produced into a long spine. 



In Lepas fascicularis the changes in appearance of the Nauplius, 

 owing to a great spinous development on its shield, are very con- 

 siderable ; and, together with its enormous size, render it a very re- 

 markable form. Dohrn (No. 520), who was the first to describe it, 

 named it Archizoa3a gigas. 



