148 C. M. CHILD. 



beyond a certain small size in open pieces is due to the slight 

 degree of local pressure exerted by the circulatory currents. 



In many open pieces the regenerating tentacles appear only on 

 a part of the oral circumference or appear later on some parts 

 than on others or grow more rapidly or to larger size on 

 some parts than on others. Figs. 9-17 afford examples of all 

 these conditions. In pieces which close and regenerate in the 

 typical manner no such differences occur. All these irregularities 

 in open pieces may be regarded as due to differences in the force 

 and volume of the circulatory currents in different intermesente- 

 rial chambers. In parts which are much contracted or tightly 

 rolled little or no water can enter, and consequently the cir- 

 culatory currents are slight or absent. The fact that in cases of 

 partial tentacle-regeneration the parts on which tentacles appear 

 are more or less distended, while other parts are collapsed, con- 

 firms the conclusion. In general, cases of this kind are similar 

 to those described in the preceding paper (Child, '04$) under 

 the head of " Local Inhibition of Tentacle-Regeneration." In 

 these cases, as in those described in that paper, it will be noted 

 that the parts most strongly contracted or folded are those which 

 fail to produce tentacles. In Fig. 9 both halves of the piece 

 become slightly distended and tentacles appear on both except 

 near the longitudinal cut where the edges are strongly inrolled. 

 In Fig. 10 only the right side of the piece is capable of retaining 

 water under pressure and only here do tentacles appear. The 

 same is true of Fig. 12, while Fig 13 resembles Fig. 9 in that 

 both sides become more or less distended. Figs. 14 and 15 

 show an interesting case in which the longitudinal cut surfaces 

 have become greatly shortened and the mesenteries bent at an 

 acute angle : these mesenteries are so closely approximated to 

 each other that little or no water can enter between them and 

 we find the tentacles corresponding to these chambers either 

 minute and delayed in regeneration or absent. In Figs. 16 and 

 17 a case is shown in which closure was long delayed and the 

 folds and wrinkles about the oral end were present for so a long 

 a time that when the piece finally did close and become distended 

 there were marked irregularities in the size of different intermes- 

 enterial chambers and consequently marked differences in rate 



