BALANIDJ2. 



33 



1. Family Balanid^e, (or Sessile Cirripedes.) 



Cirripedia without a peduncle ; scuta and terga furnished 

 with depressor muscles; other valves united immoveably 

 together. 



TABLE OF CONTENTS. 



Structure of shell 



„ of the compartments . 



„ of the radii . 



„ of the alae and sheath . 



„ of the basis . 



,, of the scuta and terga . 

 Growth of whole shell and minute 



structure of valves 

 Sack, muscles of. 

 Branchiae . 

 Thorax and body 

 Muscular system 

 Cirri, muscles of 

 Mouth 

 Cirri . . • 

 Caudal appendages 

 Alimentary canal 



Page 



87 

 88 

 93 

 95 

 97 

 97 

 100 



Page 



34 Circulatory system 



43 Nervous system 



45 Eyes and vision 



47 Acoustic organs 



49 Olfactory organs 



51 Male organs of generation . 



Female organs of generation 



54 Metamorphoses and homologies . 102 



61 Larva, first stages . . . 103 



63 Larva, last or pupal stage . .110 



65 Act of metamorphosis . . 126 



68 On the homologies of the carapace 131 



71 Cementing apparatus 



74 Classification and variation 



81 Rate of growth, exuviation, &e. . 



85 Geographical range and habitats. 



85 Geological history 



133 

 152 

 156 

 159 

 172 



.Almost every one who has walked over a rocky shore 

 knows that a barnacle or acorn -shell is an irregular cone, 

 formed generally of six compartments, with an orifice at 

 the top, closed by a neatly-fitted, moveable lid, or opercu- 

 lum.* Within this shell the animal's body is lodged ; and 

 through a slit in the lid, it has the power of protruding six 

 pairs of articulated cirri or legs, and of securing by their 

 means any prey brought by the waters within their reach. 

 The basis is firmly cemented to the surface of attachment. 

 The whole shell, basis, and operculum consists, as we have 

 already seen, of the first three segments of the head, modi- 

 fied into a singularly constructed carapace, which encloses 



* The best published description of the structure of the shell of a sessile 

 Cirripede, is given by Dr. Coldstream, in the ' Encyclopaedia of Anatomy aud 

 Physiology,' article ' Cirrhopoda.' 



ny 



