278 ZOOLOGY 
The genus /d/a 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 bathyactidis. These are 
parasitic or semiparasitic in the Actinozoa. They possess a 
large lateral carapace, into 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 
caleareous shells of Molluses and Cirrhipedes. 
(iv.) The Apoda are composed of only one genus, Pro- 
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 Rhizocephala 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 Cypris 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 
