204 



ArthropoiJa. Class 1. Crustacea. 



at the liead end, whilst it covers the rest of the body loosely ; the 

 enclosed cavity communicates with the exterior only by a slit on the 

 ventral side. In one of the chief groups of the Cirripeds, the Lepadidse 

 (Barnacles), the mantle is prolonged anteriorly into a thick, shorter or 

 longer peduncle, by means of which the animal attaches itself to 

 some foreign object. In most Lepadidae {e.g., the genus Lepas), the 

 mautle is provided externally with five calcareous plates or valves, of 

 which one, the carina, is narrow, and lies along the dorsal edge of the 

 mantle, whilst the remaining four, scuta and t e r g a, two on each 

 side, cover a larger or smaller part of the lateral surface of the mantle ; 

 that part of the surface which these plates leave bare (in Lepas, only 

 the marginal furrows between the plates, in others the greater part), 

 is covered with a thin cuticle, which also clothes the peduncle, the 

 inner side of the mantle, and the body ; the valves are specially 

 well-developed parts of the cuticle. In some Lepadidee, besides 

 these five plates, a number of large and small plates (lateralia) 

 occurs at the edge of the peduncle and the rest of the mantle 

 (Fig. 168 B). In the Balanidse (Sea-acorns), another important divi- 

 sion of the Cirripeds, the peduncle is wanting, but the animal is still 

 fixed, and indeed by the same part of the mantle as in the Lepadidae 

 the adhesive surface is large and provided with a calcareous 

 covering. The lateralia (Fig. 168 B, d), are in a line with the 



Fig. 168. Diagrammatic figures, ehcwiEg the IrsEBiticn firm Lei as ^o Ealanua 

 A Lepas, B Pollicipes, a Balanid wif.h many lateralia, d (Caiophragmus), D BaJanus 

 s peduncle, a — d valves, a scutum, 6 tergum, c carina, d lateralia. The lettering is the 

 same for all the figures. — Orig. 



carina (c), and are connected to form a hard shell, the testa, 

 which surrounds the greater part of the animal like a box. The 

 testa rarely consists of a large number of plates in several circles (Fig. 

 168 C), but more frequently of a smaller number (6 — 8) of large 

 plates in one circle {D, d — c) . A lid (operculum) for the box 

 is furnished by the rest of the mantle with the four large plates (a, b) 



