CHORD ATA 



431 



Sub-class II. Cephalodiscida. 



Chaeactekistics. — The pharynx is pierced ly one pair of gill- 

 slits. The alimentary canal has a neural flexure, so that 

 the mouth and anus are approximated. The collar hears 

 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 



■ v; .■■'•••■■«■ ■ ■. ■ ■ .'.' / 



■^^>t::'- 



Fig. 248. — Ventral view of Cephalodiscus dodecalqphus. 

 1. Tentacular plumes. 



After M'lntosh. 



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 



