CIRRIPEDIA. 



415 



group are best understood by the study of their develop- 

 ment. 



The nauplius larva (Fig. 268) is provided with the character- 

 istic three pairs of appendages and median eye, but it also 

 possesses a very delicate dorsal shield prolonged laterally into 

 two peculiar " frontal horns " to which in the later stages, in 

 Lepas, long median and lateral horns are added. The upper lip 

 is large, recalling that of the Phyllopod larva. 



After undergoing several moults in this guise the larva sud- 

 denly emerges in the Cypris stage (Fig. 269). It is enclosed in a 

 bivalve shell, the margins of which are flattened along the 

 ventral surface, and a pair of compound eyes is present in ad- 

 dition to the median eye. The anterior antennae are four- 

 jointed, and bear a characteristic disc at the end of the second 

 segment on 

 which opens the 

 duct of the 

 cement gland, 

 whose lobules lie 

 in the anterior 

 part of the body. 

 The posterior an- 

 tennae of the 

 nauplius have 

 disappeared, and 

 the man d i b 1 e s 

 and two pairs 



of maxillae are rudimentary. There are six pairs of biramous 

 and setose thoracic appendages, recalling those of Copepods. 

 The short abdomen ends- in a caudal fork. The position 

 of the animal in relation to its shell is already peculiar. The 

 mouth lies behind the middle of the ventral region and is 

 directed backwards, so that, as shown in Fig. 269, the axis 

 of the animal is bent into a U with unequal limbs. The fold 

 where the inner lining of the carapace joins the dorsal body-wall, 

 which we may call the dorsal fold, is situated on the dorsal 

 side, and some of the soft parts are included in the fold of the 

 carapace. The median eye lies a little behind the compound 

 eyes, and at the bases of the antennae the chitinous covering 

 forms two strong plates (apodemes) projecting deeply into the 



FIG. 269. Cypris larva of Lepas fasciculate, ab abdomen ; 

 pa paired eye; rf thoracic feet; ua median (nauplius) 

 eye, 1 anterior antennae. From Lang, after Clans. 



