FORM REGULATION IN CERIANTHUS ^STUARII. 49 



of regulation is involved, but merely the same complex of reac- 

 tions as in other cases under different conditions. 



From these experiments with transverse and oblique lateral 

 incisions it is evident that the formation of a lateral partial disc 

 (Figs. 14 and 15), a lateral complete disc borne on a column 

 arising like a lateral branch from the side of the body (Fig. 19), 

 the formation of a few tentacles which disappear later (Fig. 21), 

 or the closure of the wound without formation of a disc may each 

 be determined by the conditions of the experiment. These dif- 

 ferent results cannot be interpreted as in any sense purposive or 

 adaptive responses of the animal to the special conditions, since 

 the nature of the reactions themselves is not altered, but merely 

 their position, relation and sequence, and these are very clearly 

 determined by the conditions of the experiment. 



The Effect of Internal Pressure and its Absence upon 

 THE Body-Wall in General. 



As was noted above, the body-wall of this species is thinner 

 and more delicate than that of C. solitarius and very much more 

 so than that of C. meinbranaceiis. It is also much more sensitive 

 and reacts more rapidly to the mechanical conditions resulting 

 from internal pressure than do the tissues of either of those 

 species. 



Pieces of C. solitarius cut in such manner that closure is impos- 

 sible remain alive for months, though they undergo gradual de- 

 crease in size and atrophy and finally break up and disintegrate. 

 Pieces of C. cvstuarii, on the other hand, in which no distension 

 is possible, atrophy much more rapidly. The atrophy begins at 

 points where the body-wall is sharply folded, and splits and 

 breaks often occur in such regions within a week or ten days 

 after the operation. The whole piece often breaks up and disin- 

 tegrates completely in the course of three or four wrecks — some- 

 times even more rapidly. Particular regions of the body-wall 

 which remain collapsed for any considerable length of time un- 

 dergo complete degeneration and disintegration. In short, it is 

 evident that an essential condition, not only for the formation of 

 new substance, but for the continued existence of the body -wall 

 and tentacles in this species is the mechanical condition resulting 

 from distension of the enteron with fluid. 



