150 INVERTEBRATE ANIMALS. 



these are much smaller than the females, and quite different from 

 them in appearance, and they spend their existence within the shell 

 of the female. 



Greatly as the Cirripedes are metamorphosed, when compared 

 with the typical Crustaceans, they are not so entirely altered as are 

 the nearly allied animals known as the Rhizocephala. These sin- 

 gular Crustaceans are fixed parasitically to the under side of the 

 abdomen of craLs and hermit-crabs, the body being a mere muscular 

 sac, with no indications of limbs or of segmentation, attached to its 

 host by means of branched root-like processes of attachment, which 

 sink deeply into the tissues of the latter. The young of these 

 degraded Crustaceans have, however, limbs and organs of vision, 

 and swim about actively in the water. 



