FORM REGULATION IN CERIANTHUS. 2/9 



In this case, as in the growth of new tissue between diverging 

 cut surfaces described in the preceding paper (Child, '04), the 

 localization and extent of growth is dependent, not on internal 

 factors, but on simple mechanical conditions of tension. 



The figures and the details of the description given refer to 

 C. sohtarius. The process of closure and distension in C. inciii- 

 branaccus differs in some details from this, though undoubtedly 

 subject to similar conditions. It was shown in the preceding 

 paper (Child, '04) that the new tissue in C. nicuibranacens is able 

 to spread over larger areas and therefore to close larger openings 

 than in C. solitarius, and moreover, that it is thicker and more 

 resistant than in the latter species. Taking these facts into con- 

 sideration we find that the process of closure and spreading of 

 the ends is similar in both species. It is probable that the de- 

 pendence of growth of the new tissue on tension would not have 

 been so readily recognized in C. inembranaccits if this form alone 

 had been studied. The tissue after its formation is so resistant to 

 tension that the distension of the piece is very commonly insuf- 

 ficient to bring about any considerable increase in the amount of 

 new tissue after closure. Frequently, however, some growth 

 after distension is recognizable, though it is usually relatively 

 much less than in C. solitarins. This difference between these 

 species indicates the importance of comparative study of related 

 species in experimental work. Phenomena not readily interpreted 

 in one species may be modified in another so that interpretation 

 is without difficulty, and it is often possible, as in the present in- 

 stance, to apply the interpretation obtained in the one case to the 

 other, although its recognition in the first case would have been 

 difficult or impossible. 



TENTACLE REGENERATION IN RELATION TO THE MESENTERIES. 



Attention has already been called to the fact that tentacles do 

 not regenerate in the absence of mesenteries (Child, '03^). 



In regenerating ends representing levels near the oral end of 

 the parent body the series of mesenteries is complete or nearly 

 so ; farther aborally, however, mesenteries are present over only 

 a larger or smaller portion of the circumference, according to the 

 level. In the pieces from these regions a certain number of mes- 



