PHYLUM ARTHROPODA 



533 



bivalved carapace, formed by a fold of the skin, and strengthened 

 by five calcareous plates. Of these one is median and dorsal, and 

 is called the carinn (/) ; two are lateral and proximal, the scuta (s); 

 and two lateral and distal, the tcrga (t). During life the carapace 

 is partly open, and from the ventrally placed aperture delicate 

 setose filaments are protruded and keep up a constant grasping 

 movement : these are the endo- and exopodites of the biramous 

 thoracic feet, of which there are six pairs. Removal of the carapace 

 shows the feet to be attached to a vermiform unsegmented body 



L. 



Cd.. 



V 



FIG. 419. Lepas anatifera. A, the entire animal; 13, anatomy. (t\, antennule ; c. carina ; 

 cd, cement gland ; /, digestive gland ; (. adductor muscle : od, oviduct ; oc. ovary ; p. (in B) 

 penis and (in A) peduncle ; . scutum ; t. tergum and testis ; cd. vas defereiis. (From Lang's 

 nti/, after Darwin and Glaus.) 



(B), attached on the ventral aspect to the stalk and carapace by 

 its anterior end, while its posterior end is free and terminates in 

 a long filament, the penis (p), immediately dorsal to which is the 

 anus. The mouth is ventral and anterior, and is provided with a 

 pair of mandibles and two pairs of maxillae. There are no 

 antennae : at first sight the antennules appear to be absent, but a 

 careful examination shows the presence of a pair of minute 

 structures (a'} on the proximal or attached surface of the stalk, 

 and .embedded in the cement by which the animal is fixed to its 

 support ; these are the antennules, ancj their position relatively to 

 the mandibles shows that the stalk is formed by an elongation of 

 the anterior region of the head. 



