ANATOMY 



83 



which live in great numbers attached to rocks and other objects 

 between tide-marlcs, the body is constructed on a similar plan, save 

 that there is no stalk, and the body is completely enclosed in a hard 

 calcareous box formed from the mantle, which, when the valves 

 are closed, as they always are during low tide, completely protect 

 the animal inside from desiccation or danger of any kind. Besides 

 the cement-glands situated in the peduncle, we can distinguish 

 the generative organs, consisting of a pair of ovaries and testes, the 

 majority of Cirripedes being hermaphrodite. The testes open at the 

 end of an elongated median penis behind the thoracic limbs, 



Fig. 52. — A, Dwarf male of Scalpelluvi vulgare, x 27 ; B, diagram of Stalked 

 Barnacle. «, Peduncle ; al^ alimentary canal ; h, brain ; c, carina ; e, remains of 

 Nanplius eye ; gl, cement-gland ; in, mantle-cavity ; 0, its opening ; ov, ovary ; 

 p, penis ; s, scutum ; t, testis ; tm, tergum, seen in A as tlie shaded body above 

 the reference-line of e and to the right of the carina, on the left of the figure. 



while the ovaries, situated in the peduncle, have paired openings 

 into the mantle-cavity on either side of the head. A pair of 

 maxillary glands or kidneys are present, and the alimentary 

 canal is provided with various digestive glands. Special 

 branchial organs are not present in the Pedunculate Cirripedes, 

 but in the Operculate genera two branchiae are formed from 

 the plications of the internal surface of the mantle. There 

 is no contractile heart, and the circulatory system is poorly 

 developed. The Cirripedes are badly furnished with sensory 

 organs ; the remains of a simple Nauplius eye may persist, 

 situated on the upper part of the stomach, but the chief sense- 

 organs are the sensory hairs upon the limbs. 



The recent Cirripedes fall into six clearly defined Sub-orders. 



