16 Coelenterata. 



Child ( l ) describes form regulation in Cerianthus. In cylindrical pieces, ob- 

 tained by 2 transverse cuts, collapse at once occurs and the cut ends roll 

 inwards finally coming into contact and more or less completely closing the 

 opening. In 2 to 3 days a thin membrane, formed by the growth of new 

 tissue from the cut surfaces, closes the ends completely. The piece becomes 

 gradually distended with water (owing to accumulation of metabolic products 

 in the enteron and consequent diffusion of water into it), the infolded margins 

 of the body wall are forced apart by internal pressure and the area occupied 

 by the thin membrane increases. The first step in the regeneration of ten- 

 tacles is the formation of a slight marginal tentacular ridge on the oral end. 

 This ridge is formed wholly within the tissue of the old body wall , its for- 

 mation being accompanied by reduction and disappearance of the muscular 

 layer and of the pigment and great reduction in thickness. The marginal 

 tentacles first appear as upgrowths from the highest point of the ridge, 

 one tentacle above each inter-mesenterial chamber. They appear in a single 

 circle and usually with nearly equal rapidity. The directive tentacle is usu- 

 ally slightly thicker than the others (the directive chamber being larger). The 

 marginal tentacles increase rapidly in length and gradually become arranged 

 in about 3 circles, there being no longer space on the margin of the disc for 

 all of them in a single row. The disc expands and the distinction between 

 the thin membrane of new tissue and the old body wall disappears, as in the 

 latter, there is loss of the muscular layer, the pigment and thickness. The 

 mouth appears, after the marginal tentacles are well established, near the base 

 of the directive tentacle and gradually extends along the directive plane across 

 the centre of the disc until it is symmetrical; the portion first regenerated 

 being the region of the siphonoglyph. The labial tentacles do not appear un- 

 til the marginal ones have reached a length of several mm., each appears over 

 an intermesenterial chamber, but some chambers have none. After closure by 

 the new tissue the aboral end slowly acquires a conical form protruding from 

 the wrinkled margin of the old body wall. The wrinkles on the latter gra- 

 dually disappear and this is accompanied by fading of the pigment and loss 

 of the muscular layer as this region of the body wall becomes involved in 

 processes of growth and redifferentiation. The aboral end grows out into an 

 elongate conical form at the end of which the aboral pore appears. As the 

 new muscles are formed in this region pigment stripes begin to appear. 



Child( 2 ) finds that the power of regeneration from cut surfaces in Cerian- 

 tUus is greatest at the oral end and decreases aborally becoming null a cer- 

 tain distance from the aboral end. This decrease is shown by differences both 

 in rapidity and in amount of regeneration. The size of the piece does not 

 influence the rapidity or the amount of regeneration, except in the latest stages. 

 Since the regenerative power is different at various levels, the minimum size 

 of a piece capable of regeneration also varies at different levels and inversely 

 as the regenerative power. Rapidity and amount of regeneration increase and 

 decrease with the temperature. The assumption of a special regulatory mecha- 

 nism is not necessary for the explanation of form regulation in Cerianthus. 



Duerden( 1 ) describes sponge- encrusting Actinians which usually occur as white 

 or orange circular discs. Where the colony is in active growth it forms long, 

 narrow chain-like rows of polyps connected by a superficial stolon-like coenen- 

 chyme, but in older colonies the rows are broken up into small groups of 

 polyps with little intervening ccenenchyme, or the polyps may be isolated. 

 Duchassaing and Michelotti who first recognised them as zoanthid polyps, re- 

 ferred them to several diverse genera among which is the peculiar Bergia, the 



