CEPHALODISCUS. 263 



The account which we possess of Cephalodiscus forms 

 one of the Challenger Reports, and was written by Pro- 

 fessor W. C. M'INTOSH, who made out the main features 

 of its anatomy. It was further treated, from a morpholog- 

 ical standpoint, by SIDNEY F. HARMER, who pointed out 

 its remarkably close affinity to Balanoglossus. 



The most important morphological features in the anat- 

 omy of Cephalodiscus are shown in Figs. 125-127. The 

 individuals live in colonies, in a " house " or coenoecinm, 

 which consists of a ramifying and anastomosing system of 

 tubes, the walls of which are composed of a semi-trans- 

 parent, gelatinous material, whose outer surface is covered 

 with spinous projections. The walls of the ccencecium 

 are furthermore perforated by numerous apertures, which 

 allow of the ingress and egress of water. 



The adult members of a colony have no organic con- 

 nexion between themselves, but each one is independent 

 and free to wander about the tunnels of the ccencecium. 

 Although Cephalodiscus has not been studied in the living 

 condition, there is every reason to suppose that it moves 

 about in its tube by means of the large buccal shield (Fig. 

 125) overhanging the mouth, by which it can attach itself 

 to the inner surface of the tube, and then help itself 

 along by the curious pedicle which occurs ventrally near 

 the hinder end. It thus seems probable that this pedicle 

 can be used as a sucker, but its chief function lies in the 

 production of buds which grow out from it, and eventually 

 become detached. Bateson has described a somewhat 

 similar sucker at the hinder end of the body in young 

 individuals of Balanoglossus (Fig. 113). 



Behind and above the buccal shield there is a row of 

 twelve tentacles or branchial plumes, each possessing a 

 central stem or shaft which carries numerous lateral 



