26 Coelenterata. 



according to their condition. Small branches often appeared on the tentacles, 

 the origin of which the author ascribes to mechanical stimuli. Large and 

 small pieces behaved very differently in regeneration. With few exceptions 

 the large fragments produced no new zone of mesenterial formation, but a 

 wound-membrane was formed and the pedal disc and body wall simply repaired. 

 The edges of the wound contracted slowly and the borders fused, the old 

 mesenteries thus passing over into the "bud". In other cases where the pieces 

 maintained their extended condition, the stronger mesenteries, by solution of 

 their middle part, became arranged round the new storuodseum. Circular pieces 

 containing the outer part of the pedal disc and the most proximal part of the 

 body-wall developed several stornodsea so that forms arose resembling a colony. 

 The regeneration of the larger pieces with long wound-surface caused the 

 origin of various symmetries according as the piece contained directive mesen- 

 teries or not. The original position of the directives is of importance in in- 

 fluencing the final symmetry and also the formation of tentacles. New tentacles 

 were, apparently, always first protruded from the older and then from the 

 younger eutoccels. A tentacle was first formed above the directive chamber, 

 during the course of regeneration other tentacles were formed on each side 

 of the directive tentacle, a double individual with 2 groups of tentacles and 

 2 stomodsea being produced, the two parts of which possessed in common the 

 original directive tentacle. When growth was slow the piece formed only one 

 tentacle, in the wound-zone of the original directive, and so arose transition 

 forms between double forms and single animals. In larger fragments in which 

 the pair of directives did not lie in the middle of the piece, there arose, by 

 solution of the middle part of this pair, two asymmetrically placed pairs of 

 directives. Larger pieces without directives generally produced radial forms 

 and there was no new zone of meseuterial formation, but sometimes bilateral 

 forms arose; small pieces, without directives, generally produced a new 

 zone of growth. Regeneration was most typical in pieces which contained 4 

 or 8 mesenteries, more irregular in those with 2 or 16 mesenteries. The new 

 structure contained, as a rule, only 1 pair of directives and was bilateral. 

 The number of complete new mesenteries varied, often there were only 4, 

 sometimes they were not alike on the two sides of the directive plane, but the 

 two stronger mesenteries on each side of this plane were similarly orientated, 

 and their longitudinal muscles were turned towards the old part of the piece. 

 The position of the new growth zone with regard to the old part varied in 

 the pieces with 16 mesenteries, in one case the new directive plane was at 

 right angles to the median plane. In such pieces 2 regeneration zones were 

 liable to occur, only one of which, however, possessed directives. In one piece, 

 with 4 mesenteries, the regenerated zone contained 2 pairs of directives, in 

 another piece with 8 mesenteries there were 2 stomodsea. Small entocoelic 

 pieces which were cut out from the proximal part of the body-wall and outer- 

 most part of the pedal disc degenerated without regeneration. The origin 

 of various symmetries during regeneration is noteworthy because similar forms 

 are met with in nature. All accidental variations from the normal symmetry 

 in a species are to be ascribed to regeneration. Possibly regeneration has had 

 an influence on the radial symmetry of Thalassianthus, Paranemonia contarini 

 and Gyractis, and also on the bilateral symmetry of embryos. In the latter 

 case the dorsal siphouoglyph and dorsal directives arose through regeneration. 

 The author also deals with natural laceration in Metridium dianthus and 

 Aiptasia diaphana. The bilateral symmetry so frequently met with in M. may 

 be traced to regeneration in pieces (which originally contained no directives) 



