FORM -REGULATION IN CERIANTHUS. 143 



December 2 : Marginal tentacles 6-7 mm. on uncut side, 30 

 mm. on cut side ; labial tentacles present on uncut side, absent 

 on cut side (Fig. I 5). 



December 12 : Marginal tentacles 10 mm. on uncut side, 5-0 

 mm. on cut side, etc. 



No. 6. December 2 : Apparently not yet fully closed by new 

 tissue, but slightly distended ; marginal tentacles 2-3 mm., blunt 

 and sac-like. 



December 12: Apparently closed, distended; one marginal 

 tentacle 5 mm., others 2-3 mm.; labial tentacles just appearing. 



December 24 : Marginal tentacles irregular in length, 36 

 mm., labial tentacles 12 mm., etc. 



No. 7. December 6 : Closure by new tissue not complete, but 

 slightly distended, some marginal tentacles 2 mm., sac-like, others 

 mere buds (Fig. 16). 



December 1 2 : Closed and distended. Marginal tentacles very 

 irregular in length, 1-6 mm., absent near region of cut; a few 

 labial tentacles just appearing (Fig. 17). 



December 24: Marginal tentacles 37 mm., absent near cut; 

 labial tentacles 12 mm. on uncut side, a few absent on cut side. 



No. 8. December 24 : Closed and distended. Marginal ten- 

 tacles 4-5 mm., quite regular; labial tentacles I mm., a few 

 absent near region of cut. 



January 21, 1903 : Little change since December 24. 



No. 9. January 2 I : Apparently closed, but distension slight, 

 probably because of low temperature, slime, and continued star- 

 vation ; marginal tentacles 1-3 mm., mostly 3 ; labial tentacles 

 I mm. 



In this series the close relation between the internal water- 

 pressure and growth of the tentacles is evident. Although the 

 marginal tentacles appeared as minute buds before marked dis- 

 tension occurred, they did not advance beyond this condition in 

 any case until the water-pressure increased in some cases a 

 period of more than three months. As soon as distension took 

 place the tentacles continued their regeneration. This series con- 

 stitutes a demonstration of the role of water-pressure as a factor 

 in the regeneration of the tentacles, but does not throw any addi- 

 tional light upon the problem of their origin and localization. 



