IO6 C. M. CHILD. 



ever, is this : when the lateral cut is only slightly aboral to the 

 cesophagus the intermesenterial chambers oral to the cut may be 

 closed temporarily and so the tentacles corresponding to them 

 may remain less distended than the others as long as this condi- 

 tion continues. This difference is due simply to mechanical 

 plugging of the openings of the intermesenterial chambers at the 

 aboral end of the oesophagus and the consequent exclusion ot 

 water. As soon as the cut is actually closed by new tissue the 

 increasing distension causes stretching of the body-wall and mes- 

 enteries and the closure of the chambers can persist no longer. 

 The tentacles in this region now become as fully distended as the 

 others and since the period of their collapse is usually short in 

 such cases, are soon equal in length to the others. If the inter- 

 mesenterial chambers remain contracted and plugged during a 

 long time considerable reduction of the corresponding tentacles 

 may occur. Cases of this kind have occurred frequently among 

 my specimens and it was always evident that the contracted con- 

 dition of parts about the cut and especially oral to it was respon- 

 sible for the absence of distension in tentacles oral to this region. 

 If the collapse were osmotic in nature, as Loeb believes, there is 

 no reason apparent why it should be permanent when the cut is 

 in the cesophageal region and only temporary when the cut is a 

 few millimeters lower. 



Loeb found that lateral cuts in the middle and aboral regions 

 showed a much greater tendency to close by union of their mar- 

 gins than those near the oral end. He does not attempt to ac- 

 count for this difference in any way, but the reason is evident at 

 once when the part played by the cesophagus is understood. In 

 the cesophageal region the cut margins of cesophagus and body- 

 wall almost always come into contact in consequence of the in- 

 rolling (Fig. 2). The distension following union of the parts 

 prevents the two cut surfaces of the body-wall from coming into 

 contact with each other and, therefore, they never unite and an 

 opening remains which is in reality a new mouth. If they hap- 

 pen to come into contact with each other instead of with cesoph- 

 ageal cut edges they unite but the usual result is determined 

 by the fact that conditions are much more favorable for the union 

 of body-wall and cesophagus than for body-wall and body-wall. 



