380 THE INVERTEBRATA 



opens a unicellular gland (see Fig. 258). These are processes of a 

 dorsal shield which in later stages acquires other spines. After several 

 moults the larva suddenly passes into the so-called Cypris stage. It is 

 now enclosed in a bivalve shell with an adductor muscle, and possesses 

 a pair of compound eyes. The antennules of this stage possess near 

 their ends a disc on which opens the cement gland. The antennae have 

 disappeared. There are six pairs of biramous thoracic limbs and a 

 small abdomen of four somites. The Cypris larva becomes fixed by 

 the discs on its antennules, and its body rotates within the shell, so 



M ' I I 

 th. M. e! e. an'. 



scu. 



na. 



B 



Ih. e'. CC' al. y- an'. 



Fig. 256. Diagrams of three stages in the metamorphosis of Lepas. From 

 Korschelt and Heider. A, The Cypris stage. B, The attached larva (pupa). 

 C, The young Lepas. ab. abdomen; al. aHmentary canal; an.' antennule; 

 car. cuticle of carapace of larva, not yet shed; cna. carina; e. compound eye; 

 e.' median eye; M. mouth; scu. scutum; tgm. tergum; th. thoracic limbs; 

 X. origin of carapace fold ; y. a ventral fold of the head. 



that the ventral surface is directed backwards (Fig. 256 A, B). Now 

 the shell and body are rotated upwards on the antennae so that the 

 adult position is assumed (Fig. 256 C); meanwhile the shell plates 

 appear, the preoral region elongates to form the peduncle, and the 

 abdomen disappears. 



Scalpellum (Fig. 257 C, D) attaches itself to fixed objects, usually 

 in deep waters. It diff^ers from Lepas in possessing a number of ad- 

 ditional plates on the capitulum, and scales of a similar nature on the 

 peduncle. It is more remarkable in possessing what are known as 

 complemental males . A few species of the genus are composed entirely 



