214 



CRUSTACEA. 



by the casting of the Metanauplius integument, emerges from the- 

 preceding stage. 



The free-swimming Cypris stage (Fig. 104), which is only of short 

 duration, derives its name from the bivalve shell that envelops the 

 whole body. The actual segmentation of the body and the inner 

 organisation have nothing in common with the Ostracoda. In 

 respect to these the larva at the Cypris stage already very nearly 

 approaches the adult. The two shell-valves which can be brought 

 together by an adductor muscle, are directly continuous dorsally. 

 The dorsal border appears arched, whereas the ventral edge is- 

 flattened. Anteriorly they are rounded, but run out to a point 

 posteriorly. In the anterior section of the valves, near the ventral 

 side, a small projection may be remarked on which can be recognised 

 the frontal horn of the Nauplius. The ventral margins of the shell 

 are closely approximated in the middle of their length. Posteriorly r 

 a fissure opens between them for the passage of the swimming limbs 



of the larva 

 (rf), and there is 

 also an anterior 

 aperture through 

 which the first 

 antennae, the 

 adhesive organs 

 (/), are protruded. 

 The latter limbs, 

 in the free Cypris 

 stage, are used 

 for the occasional 

 attachment of 

 the larva, which 



precedes and prepares the way for the final attachment. They consist 

 at this stage of four joints, the basal joint joining the body by a broad 

 base, and carrying various chitinous ingrowths (apodemes) for the 

 attachment of muscles. The second joint, which is lengthened like 

 an arm, is bent at an angle to the basal joint. The short third joint 

 carries at its outer side the adhesive disc, at the centre of which the 

 duct of the cement-gland opens, while the truncated fourth joint 

 seems to be provided with one ordinary and one large olfactory seta 

 (GLAUS, No. 39 ; WILLEMOES-SUHM, No. 62). 



The cement-gland (Fig. 105, cd) shows various degrees of develop- 

 ment in the Cypris larva. In the pupal stage which follows, it 



rf 



FIG. 104. Cypris-like stage of Lepas fascicularis (after GLAUS, from 

 LANG'S Text-book), ua, Nauplius eye ; pa, paired eye ; rf, thoracic 

 (swimming) limbs ; ab, abdomen ; I, first antenna. 



