CIRRIPEDIA. 



419 



understood (Figs. 272 and 273) is made up of the hollow muscular 

 peduncle or stalk, containing the ovaries and the remains of the 

 cement gland, and of the capitulum. The latter consists of the 

 mantle, or dorsal shield, with its calcareous valves, together with 

 the contained body, which is pear-shaped and formed, as we 

 have seen, from part of the cephalic region of the larva, to- 

 gether witli the thorax and rudimentary abdomen. The valves 

 of the shell of the Lepadidae consist of a pair of large scuta (Sc) 

 situated anteriorly, posterior and dorsal to them of a pair of 

 terga, and of a single median and dorsal carina (C). The narrow 

 end of the piriform body is divided by grooves into segments 

 bearing the five posterior pairs of thoracic appendages. In front 

 is the rounded and unsegmented prosoma bearing the first pair 

 of thoracic and the oral appendages. It is connected with the 

 mantle for a short distance in front of the mouth, and through 

 this region passes transversely the great adductor scutorum 

 muscle (Fig. 273, M). 



Various modifications of the outer form 

 of the body are met with. In Concho- 

 derma the mantle remains to a large 

 extent membranous, the valves being 

 reduced in size. In Anelasma, which 

 lives embedded in the skin of sharks, the 

 valves are absent, and rootlike processes 

 extend into the tissues of the host from ot 

 the peduncle. The Pollicipedidae are j 



transitional between the simple condition 

 of Lepas and that presented by the Bala- 

 nidae. In addition to five mantle plates 

 homologous with those of Lepas, small 

 calcareous plates are developed, in the 

 cuticle of the peduncle, and larger accessory 

 plates at the base of the capitulum. Among 

 the latter a median ventral plate, the 

 rostrum, is situated opposite to the dorsally 

 placed carina. 



In the Balanidae the carina together 

 with the accessory (side) plates form the 

 outer ring constituting the testa of this 

 family. The carina, detached in this 

 family from the true mantle, and the 

 rostrum lie at either end of the median 

 plane, and side plates are present in vary- 

 ing number (carino-lateral, lateral and 

 rostro-lateral) overlapping one another at their sides. The scuta and terga 

 on the other hand retain their position on the mantle covering the mov- 

 able posterior part of the body, and together form the two halves of the 



FIG. 273. The organization of Le/ms, 

 after removal of the integument. 

 (After Claus.) References as in Fig. 

 272. 



