FORM REGULATION IN CERIANTHUS /ESTUARII. 45 



enteric cavity again become open and fill with water and renewed 

 distension of the tentacles and consequently renewed growth 

 occurs. 



But the most interesting feature of these cases is that, so far as 

 my observations go, the lateral component is permanent and does 

 not undergo further regulation ending in union with the parts of 

 the terminal disc which remain, as do the transverse and less 

 oblique lateral discs. Some specimens were kept under observa- 

 tion during four months and at the end of this time there was no 

 indication of any further regulation leading to fusion of the lateral 

 component with the rest of the body. Fig. 19 is drawn from 

 one of these specimens four months after the operation. This 

 length of time is more than sufficient for the migration of the 

 lateral disc to the oral end of the whole if it were to occur, but 

 there is no evidence of any such change in position. Each 

 component maintains its form and relations to the other. The 

 only changes noted in later stages were, the increase in length of 

 the lateral component, which would probably in time have reached 

 the level of the original disc, the gradual reduction of the obliquity 

 of the disc of the lateral component and new growth of the 

 previously atrophied old tentacles above the cut. 



The reason for the failure of the lateral disc to migrate to the 

 oral end of the body and take the place of a part of the original 

 disc lies in the simple fact that no part of the region distal to the 

 cut underwent complete atrophy. Atrophy began, but the regu- 

 latory process involved in the filling of the area of the cut with 

 new tissue brought about the opening and renewed distension of 

 the interseptal chambers in this region and so determined its per- 

 sistence. Evidently the presence of active non-atrophied parts 

 distal to the lateral component prevents its migration to the oral 

 end. 



These cases are of considerable interest in that they indicate 

 very clearly the dependence of "normal " proportions and posi- 

 tions of parts upon certain factors which are subject to experi- 

 mental control, viz., in this case the direction of the incision and 

 the distension or absence of distension of certain parts with water 

 and their consequent persistence or atrophy. 



