174 INTRODUCTION TO ZOOLOGY " CHAP. 



fringed with hairs. The second pair is small and difficult to 

 detect. 



The body ends in two long processes, which are said to be 

 used in cleaning the shell. They often project from the 

 body when the Cypris is swimming. 



There is another little form, Candona, which is very similar 

 to Cypris in structure, but which lives a far less active life, 

 usually creeping over the mud at the bottom of a pond. It 

 can be distinguished from Cypris by the absence of the 

 conspicuous tuft of hairs on the second antennae, which 

 characterises the latter. 



In both these genera, parthenogenetic reproduction seems 

 the rule. In many species, males have never yet been 

 discovered. 



Order 4 : CIRRIPEDIA 

 BARNACLES OR CURL-FOOTED CRUSTACEANS 



The commoii Acorn Barnacles (Balanus tintinna- 



Ba^nades bulum) are probably well known to all, for to 



' them belong the hard, sharp-pointed, conical shells 



that are so plentiful on our shores on rocks and timber 



near high tide mark. This species may be an inch high. A 



much smaller species of Balanus 

 often completely covers the 

 rocks. 



When exposed at low tide, 

 these shells can easily be ob- 

 tained by chipping off a piece 

 of the rock on which they grow : 

 if then transferred to a bowl of 

 sea-water their structure can be 

 investigated. 



The shell is calcareous, and is 

 composed of a hard base fixing 



it to the rock, from which stands 

 FIG. lll.-Acorn Barnacle (Balanus}, up ft ring of gix more Qr lesg 

 attached to a rock, external view. A . 



triangular pieces ; these are 



fused together laterally, and the top is protected by four 

 smaller movable plates. Inside this case the animal can lie 



