HEMICHORDATA 



CHAP. 



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 Ehabdopleura 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. Cepha- 

 lodiscus forms a gela- 

 tinous " house " (Fig. 

 9, A), in the passages 

 of which are found 

 large numbers of the 

 free individuals, to- 

 gether with their 

 eggs and embryos. 



FIG. 10. Longitudinal median section of Cephalodiscus 

 dodecalophus. a, Anus ; b.c\ b.c z , b.c 3 , first, second, 

 and third body-cavities ; int, intestine ; m, mouth ; 

 nch, notoehord ; n.s, central nervous system ; oes, 

 oesophagus ; op, operculum, the ventro-lateral part 



of the collar ; ov, ovary 

 ph, pharynx ; p.p, proboscis-pore ; ps, proboscis ; st, 

 stomach ; stk, stalk. 



ovd, pigmeuted oviduct ; RhaMopleum (Fig. 



12) is protected by 

 cylindrical tubes, one 

 of which corresponds with each individual. 



Cephalodiscus, 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. 1 0, ps) 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 (2 } -P\ 

 just in front of the tip of the notoehord (ncli). The collar, 

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



