582 BIOLOGY. 



ment. Here belong the Balani and Lepades Fuss- 

 kracken. 



These animals are likewise sessile, at least when full 

 grown, and are surrounded by shell-plates, which remind 

 us of the Echini or Sea-Urchins, whose antetypes they 

 are ; this resemblance is particularly distinct in the 

 Balani, which have similar odontoid valves upon the 

 aperture or mouth of the shell. These animals also 

 undergo a metamorphosis, since in the early periods of 

 their existence they swim about like small Crustacea, 

 and later on become fixed or sedentary, and surrounded 

 by the plates of shell. 



The Lepades have the ordinary shells of Mollusca, but 

 each of the two valves consists of two pieces, between 

 which an odd one is interposed down the back. 



These five shell-pieces become in the Balani a regular 

 set of teeth, which are adherent within the cylindrical 

 shell, by which the posterior part of the body, or the 

 peduncular and elongated mantle, is surrounded. (Vid. 

 Oken's ' Allgemeine Naturgeschichte/ V, 1835, 509.) 



They bear a resemblance to the Crustacea, not simply 

 in the annulate horny feet, but also in the double and 

 ganglionic nervous chord lying along the abdomen ; only 

 they are androgynous, which occurs in no Crustacean. . 



Order 2. Conchozooid Kracken Kopfkracken. 



Tentacula upon the head or fins upon the body. They 

 repeat the Conchozoa or Shell-animals. 



Fam. 4. Mussel- Kracken JBrac&wpoda. 



The body is surrounded by a mantle open above, and 

 by two shells ; on the sides of the mouth there are two 

 arms. 



These animals look exactly like Bivalve Mollusca ; 

 they are firmly adherent to rocks, being frequently sup- 

 ported upon a hollow pedicle, which is a prolongation of 

 the mantle. Branchiae and sexual parts but little known ; 

 species probably androgynous Armkrackcn. 



3500. In the following families the body is free and 



