24 



HEMICHORDATA 



supposed. There is evidence derived from the results of the 

 " Siboga " expedition that abyssal animals may migrate into 

 comparatively shallow water in the Malay Archipelago. 



Cephalodiscus and BJiabdopleura are remarkable for their 

 power of producing buds. In the former these arise from the 



apex of a stalk which 

 is given off on the 

 ventral side of the 

 body, and they break 

 off when they reach 

 a certain age ; in the 

 latter they do not be- 

 come free, and a colony 

 results, which consists 

 of a creeping " stolon " 

 from which vertical 

 branches are given off 

 at intervals, each end- 

 ing in an individual 

 of the colony. Ceplia- 

 lodiscus forms a gela- 

 tinous " house " (Fig. 

 9, A), in the passages 

 of which are found 

 large numbers of the 



Pig. 10. — Longitudinal median section of Cephalodiscus fj'ge individuals to- 

 dodecalojjhus. ii, Anus ; b.c\ b.c\ b.c', drat, second, . . ' , 



and third body-cavities ; int, intestine ; m, mouth ; gether With their 



nch, notoohord ; «,s, central nervous system ; oes, eo-o-s and Bmbrvos 

 oesophagus ; o/j, operculum, the ventro-lateral part '"^ uxyub. 



of the collar ; ov, ovary ; ovd, pigmented oviduct ; Rhahdopleurci (Fig. 



l'mtrr.'.iS,r'"""'°"^^"^™'""^^''' ^2) is protected by 



cylindrical tubes, one 

 of which corresponds with each individual. 



CephalodisciLS, though no more than two or three millimetres 

 in length, is provided with practically all the important organs 

 possessed by Balanoglossus. Its proboscis or "buccal shield" 

 (Fig. 10, j9s) is a large flattened structure, which overhangs and 

 entirely conceals the mouth. The anterior body -cavity opens to 

 the exterior by two symmetrically placed proboscis-pores {p.p), 

 just in front of the tip of the notochord {ncli). The collar' 

 which has paired body-cavities, is produced dorsally into 4-6 



