7. Anthozoa (incl. Hydrocorallia). A. Zoantharia. 47 



(a) qualitative axial or polar differences in restitution (heteropolar phenomena): 

 the same cells may produce qualitatively different structures according to their 

 position at one or other pole; (b) qualitative regional differences (primary hetero- 

 morphosis) : short pieces from near one pole may produce the structures of that 

 pole at both ends; (c) quantitative axial or polar differences: the heteromorphic 

 structure is often delayed ; (d) quantitative regional differences : the rapidity of 

 restitution, and the size and completeness of parts decrease as the distance between 

 the level at which they form and the similar pole of the original individual 

 increases. These phenomena may be complicated and altered by the greater 

 differentiation and consequent decreased powers of restitution of certain parts, 

 the external conditions, the centralisation of the nervous system, etc. The 

 regional differences in restitution are determined by the structural polarity 

 existing in the original individual. The axial or polar differences are deter- 

 mined by the correlations between the parts of the piece after isolation; they 

 are the result of the physiological polarity. 



Child( 3 ) describes the formation of rings from short cylindrical pieces of 

 the body of Harenactis by the union of the two ends about the whole circum- 

 ference. This can be induced experimentally by removing from the piece the 

 stomodaeum (if present) and a part of the mesenterial organs. The shorter the 

 piece, the more likely it is to form a ring in closing; when the length is less 

 than the diameter a ring is usually formed or closure does not take place. 

 After closure the ring commonly undergoes a revolution about a circular axis 

 so that the union between the ends lies at or near the equator on the outer 

 surface. In some cases regulation goes no further but usually one or more 

 groups of tentacles appear at or near the line of union and show various de- 

 grees of approach to radial symmetry. The localisation of the groups of ten- 

 tacles is irregular and probably due to the different degrees of injury to the 

 parts. The tentacles may arise, some from the original oral end of the piece, 

 some from the aboral, and some from both together; or the whole group arises 

 on the oral side. The degree of injury and the original polarity are probably 

 the determining factors here. The formation of the tentacle-groups involves 

 the establishment of a new polarity (the original polarity disappears in con- 

 sequence of the union of the ends) and, in some degree, of a new radial sym- 

 metry, due to the local factors where the groups appear. 



Child ( 4 ) describes experiments on the production of partial discs in Harenactis. 

 If a lateral incision is made through the body wall into the stomodseum, the cut 

 surfaces of body wall and stomodseum unite so that a new lateral opening into 

 the stomodseum is formed. After healing, tentacles appear below this (as in 

 Cerianthus] and later also above (not in Cer.}. In the region distal to the 

 opening the intermesenterial chambers are completely shut off longitudinally from 

 the rest of the coelenteron. The presence or absence of transverse communi- 

 cation depends on the position of the cut. If this was distal to the ostia (there 

 is an ostium in each mesentery of H. about the level of the middle of the stomo- 

 dseum) each chamber is completely isolated, if proximal to the ostia then all 

 communicate with each other and with the general coelenteron. In the former 

 case distension of the body with water has no effect on the portion distal to 

 the incision and this rapidly atrophies, while the partial disc below has attained 

 the same level as the other parts of the old disc. The atrophied region forms 

 a narrow strip across the mouth, breaks, and its two ends are either cast off or 

 resorbed, leaving a normal disc. But if the cut was proximal to the ostia the 

 region distal to it is as fully distended as the rest of the body, the old tentacles 

 on this part do not atrophy and the heteromorphic tentacles on it become as 



