TYPE CRUSTACEA. 399 



Ostracode and hence termed the Cypris-stage (Fig. 180). 

 The body is enclosed in extensive folds of the body-wall 

 termed the mantle, and the antennules (at 1 ) are characterized 

 by being directed forwards and terminating in an adhesive 

 disk upon which open the ducts of cement-glands. Adher- 

 ing to a foreign body by these disks, the adhesion being 

 made permanent by the secretion of the glands, a rotation of 

 the body upon the antennae through 90 takes place, so that 

 the animal comes to lie upon its back, the ventral surface 

 looking away from the point of fixation. The antennules 

 persist as rudimentary structures, and the adult animal really 

 seems to be fixed by the dorsal surface of the head, which 

 may elongate to form a stalk bearing the body proper at its 

 extremity (Lepas, Fig. 181). 



The body shows no indication of segmentation, but a head 

 region may be distinguished from the thorax and this from a 

 short abdomen by means of the appendages. The character 

 of the anteuuules has already been mentioned ; the antennae 

 are wanting in adults, and the mandibles and first maxillae 

 are simple toothed plates destitute of palps, while the second 

 maxillae are small and fused together to form a kind of lower 

 lip. The thoracic appendages (Fig. 181, -5) are biramous, the 

 basal portion supporting two long multiarticulate and usually 

 setose filaments. In typical cases six pairs of these append- 

 ages occur, but they may be reduced to four (Alcippe) or 

 three pairs (Cryptophialus). In the living animal flexions of 

 these appendages towards the ventral surface of the body 

 take place almost rhythmically, currents of water being thus 

 impelled towards the mouth together with any food-particles 

 they may contain. The abdomen does not bear appendages, 

 but from it arises a long slender cirrus (Fig. 181, B, cir) which 

 contains the terminal portions of the vasa deferentia. 



The mantle-folds which occur in the Cypris-larva persist 

 in the adult, and calcification of their walls takes place, giving 

 rise to a calcareous shell, composed of several pieces, which 

 encloses the animal. In the genus Lepas, the goose-barnacle, 

 this shell consists of five pieces. On the dorsal side there is 

 a single unpaired piece which receives the name of the caritnt 

 (Fig. 181, A, car) ; at the sides and resting below on the upper- 



