124 



ANIMAL PHYSIOLOGY. 



[LESSON 35. 



571. The Cirripeds (meaning curled feet) are divided into two 

 orders : those having a peduncle as an organ of attachment, are the 

 Lepads, and those which are sessile (sitting close upon the body), are 

 the Balanoids. The first, are commonly called Barnacles; the 

 second, Acorn-shells. 



572. The visceral mass in this class is usually protected by a 

 calcareous shell composed of several pieces ; but in Otion cornuta, 

 the viscera is protected by the development of a horny sheath. 



573. In the common Barnacle (Lepas anatifera), found so 

 abundantly adhering to ships' bottoms, the calcareous matter extends 

 from five centres, so as to afford protection to the whole body : the ce- 

 phalic pair of valves is the largest. All the valves are strongly marked 

 with lines of growth, formed by successive additions to their margins. 



574. The sessile Cirripeds (Acorn-shells) are defended by a 

 multivalve shell j the base of which is generally formed by a calca- 

 reous plate, and the walls are apparently divided into twelve conical 

 compartments, six of which rise from the margin of the base and 

 terminate in a point at the free margin of the shell ; whilst the 

 other six, in the form of inverted cones, occupy the interspaces of 

 the preceding series. 



575. One illustration of the structure of a Lepad will suffice : 



animalcules, or other proper 

 food, are brought to the 

 mouth (a, Fig. 206) by the 

 cirrigerousfeet (6), and seized 

 by the lateral jaws; they 

 are then conveyed by a short 

 oesophagus to a dilated stom- 

 ach (c), which receives the 

 ducts of two salivary glands 

 (&). Groups of hepatic coaca 

 are developed from the walls 

 of the stomach. The intes- 

 tine (d) is bent upon the 

 stomach, and tapers with a 

 slightly sinuous course to ter- 

 minate at (e), the base of the 

 caudal appendage (/). In 

 these pedunculated Cirripeds, 

 slender conical branchiae (g) 

 are attached to the base of 

 the maxillary foot, and to that of some of the cirrigerous feet. 



FIG. 206. 



Lepas vitrea. 



