FORM REGULATION IN CERIANTHUS /ESTUARII. 33 



Experiments along this line on C. astnarii confirm my earlier 

 work. It was possible to control the development of the ten- 

 tacle in this species within wide limits : in some experiments, for 

 example, they attained a length of i mm. in the open pieces 

 while in the controls they reached the length of 15 mm. in the 

 same time. 



{p) Pieces frovi tJie Oesophageal Region. 



The CESophagus in Ceriantliiis extends a considerable distance 

 aborally from the mouth (Fig. i), and pieces in which the oesoph- 

 agus extends through the whole length can readily be obtained. 

 The process of closure of the cut ends in such pieces was de- 

 scribed for C. solitariiis in my earlier paper (Child, 'o\d, pp. 205- 

 206, Figs. 7-15), and is similar in C. iustiiarii. In almost all 

 cases the cut ends of oesophagus and body-wall unite at both 

 ends of the piece and the oesophagus therefore opens to the ex- 

 terior at each end but does not communicate with the enteron, at 

 all. In these pieces water can pass into the enteron only through 

 the body-wall, but distension by this means does not continue indefi- 

 nitely (Child, '04^/, pp. 206, 211) and after a few days the pieces 

 gradually collapse and never become distended again. Under 

 these conditions the development of the tentacles begins but 

 ceases as the distension decreases, and later, when the piece be- 

 comes completely collapsed, the tentacles undergo atrophy (Child, 

 '04^, pp. 207-212). The results of experiments of this kind on 

 C. cusUiarii are even more striking, for the atrophy occurs more 

 rapidly. The records for two series of experiments are given by 

 way of illustration. 

 Series i^. 



August JO, Tpoj. — I. A piece with oral end about the middle 

 of the oesophageal region (a, Fig. 3) and aboral end just distal to 

 the aboral end of the oesophagus (d, Fig. 3). 



II. As control a piece from another animal with oral end as 

 nearly as possible at the same level as that of I., and with aboral 

 end just proximal to the aboral end of the oesophagus (r. Fig. 3). 



The difference in length of the pieces is very slight and both 

 are far above the minimal size of pieces capable of complete 

 restitution. 



Septe7nber J. — I. Body-wall and oesophagus united at both 



