CHORDATA 431 
Sub-class I]. CEPHALODISCIDA. 
CHARACTERISTICS.— The pharynx is pierced by one pair of gill- 
slits. The alimentary canal has a neural flexure, so that 
the mouth and anus are approximated. The collar bears 
twelve tentacular plumes, which are hollow ; their cavities are 
continuations of the collar cavity. 
This sub-class contains one species, Cephalodiscus dode- 
calophus, which, owing to Harmer’s researches, has been 
AG 
4 i \ ; i: 
i 
Fic. 248.—Ventral view of Cephalodiscus dodecalophus. After M‘Intosh, 
1. Tentacular plumes. 
2. Bud at the end of pedicle, two others are also shown. 
3. Proboscis. 
associated with Balanoglossus, and placed in the group Hemi- 
chordata. Cephalodiscus is an organism which reproduces by. 
budding, and it has a certain superficial resemblance to some 
Polyzoa, but it shows closer affinities to Balanoglossus in its 
internal anatomy. It resembles the last-named genus in the 
