Factors of Form Regulation in Harenactis Attenuata 491 

 III REGIONAL FACTOR IN ORAL RESTITUTION 



I The Lnnits of Restitution and the Limits of Experiment 



The high degree of contractiHty of the body-wall, and the vol- 

 ume of the mesenterial organs constitute together an obstacle 

 to the isolation of small pieces of the body of Harenactis. In the 

 middle region of the body, between the oesophagus and the attenu- 

 ated aboral region it is usually impossible to obtain normal restitution 

 from pieces of less than one-third or one-fourth ofthe whole length of 

 the body. In such pieces a wound is present at each e-nd and the 

 immediate wound-reaction is so violent that the mesenteries and 

 muscles are forced out of one or both ends of the piece by the 

 contraction following the wound, and form a plug preventing 

 closure, or die and disintegrate and apparently infect other regions, 

 or occasionally the whole piece turns mside out and remains in 

 that condition until death. If the protruding plug be cut off 

 the stimulation produces further contraction and other masses of 

 the mesenterial organs take the place of those removed. The 

 result of the removal of all these organs, viz: the formation of 

 "rings" (Figs. 14 and 15) has already been mentioned. In 

 the oesophageal region short pieces with a wound at each end 

 often extrude the oesophagus. All of these conditions make it 

 practically impossible to determine the regulatory capacities of 

 most regions of the body by isolation of small pieces. The phe- 

 nomena in rings, which will be described later, afford good reason 

 for believing that even very small pieces of the body are physio- 

 logically capable of complete restitution, but usually fail to under- 

 go such restitution simply because closure of the wound is physi- 

 cally impossible after the extrusion of the enteric organs. In the 

 attenuated aboral region the volume of the enteric organs is not 

 great and closure of the wound usually occurs even in very short 

 pieces. Here, however, as will appear below, the physiological 

 capacity is lacking or very much less than elsewhere and restitu- 

 tion is much retarded, or does not occur at all. 



In pieces with a wound at only one end, i.e., pieces possessing 

 the original oral or aboral end, the contraction following the wound 



