Form Regulation in Harenactis 69 
may attain the same length as the others (Child, ’oga), otherwise 
both they and the tentacles directly distal to them at the original 
oral end undergo gradual atrophy and the whole strip finally dis- 
appears as in Cerianthus. 
6 
Fig. 3 Oral region of body in longitudinal section: dotted line indicates the operation for produc- 
ing lateral mouths. 
Fig. 4 Early stage after the operation indicated in Fig. 3. 
Fig. 5 A later stage, showing heteromorphic tentacles above the lateral opening. 
Fig. 6 Surface view from side, showing lateral mouth with normal tentacles below and hetero- 
morphic tentacles above. 
In these cases then a partial aboral disc is formed distal to the 
lateral opening and a partial oral disc with the same number of 
tentacles—except in cases of irregularity of closure—develops 
