278 ZOOLOGY 



The genus Ihla presents only the latter two of these degrees 

 of sexual differentiation. 



The remaining groups of Cirrhipedes are parasitic, and 

 have undergone considerable degeneration. 



(ii.) The Ascothoracica consist of three species: Laura 

 gerardiae, Synagoga mira, and Petrarca bafhyactidis. These are 

 parasitic or semiparasitic in the Actinozoa. They possess a 

 large lateral carapace, iato which the digestive and repro- 

 ductive organs extend, a condition of things characteristic of 

 Ostracods ; in other essential respects they resemble the 

 Cirrhipedes. 



(iii.) The Abdominalia include the two genera Alcippe and 

 Cryptophialus. They are unisexual, and in the former the 

 male is dwarfed. They live parasitically, boring into the 

 calcareous shells of Molluscs and Cirrhipedes. 



(iv.) The Apoda are composed of only one genus, Fro- 

 teolepas. It has a maggot -like body consisting of eleven 

 segments, and has no thoracic or abdominal limbs. The 

 mouth is a sucking one, and its appendages are present ; the 

 alimentary canal is rudimentary. It lives within the mantle 

 of other Cirrhipedes, and seems to be truly parasitic, living on 

 the juices of its host. It is hermaphrodite. 



(v.) The Ehizocephala comprise a few genera which are 

 parasitic chiefly on Crustacea. They have reached an 

 extreme stage of degeneration, their body being rounded, 

 and without any trace either of segmentation or of appendages. 

 No alimentary canal exists in Sacculina, which is frequently 

 to be found on the abdomen of Carcinus moenas or other crabs; 

 the alimentary canal is not present even in the Nauplius 

 larva. This genus, like so many other parasitic Cirrhipedes, 

 attaches itself to its host in the Gypris stage, fixing itself on 

 the carapace or legs just at the origin of a hair where the skin 

 is soft. It usually chooses some young individual in which 

 the integument has not yet completely hardened. The Cypris 

 fixes itself at first by means of its first pair of antennae, it 

 then moults and throws off its skin, and the cellular body of 

 the Sacculina now migrates through the cavity of its antenna 

 into the body of the crab. It then makes its way to the 

 intestine and comes to rest in that region of the body where 



