REGULATION OF HARENACTIS ATTENUATA. 5 I 



Observation of such cases in distended and collapsed condition 

 establishes the fact that changes in the degree of distension of 

 other regions do not alter the distension in the region directly 

 distal to the incision. In all such cases this region acquires a 

 certain degree of distension after healing of the wound, un- 

 doubtedly in consequence of the passage of water through the 

 walls, but this distension gradually decreases as time goes on until 

 finally collapse is complete. 



The condition of such animals three to four weeks after the 

 operation is indicated in Fig. 4. The region distal to the cut has 

 undergone rapid atrophy and the partial disc below it has at- 

 tained the same level as other parts of the old disc. The atrophied 

 region is now completely collapsed and in an oral view of the 

 animal forms merely a narrow strip across the disc with a mouth 

 opening on each side of it. 



A little later this strip breaks and its two ends become still further 

 reduced and soon undergo complete resorption or in some cases 

 drop off, leaving a normal disc. 



The result is very different when the incision is made proximal 

 to the level of the ostia, e.g., at b, Fig. I, or any level proximal 

 to this within the cesophageal region. In such cases (Fig. 5) 

 the old tentacles distal to the incision do not undergo atrophy 

 and the heteromorphic tentacles become almost or quite as long 

 as the others. Moreover, examination of the specimen shows at 

 once that the whole region distal to the incision is as fully dis- 

 tended as other parts of the body when the animal is undis- 

 turbed, and when contraction and expulsion of water occurs this 

 region takes part in the change, becoming distended again when 

 other parts of the body distend. Fig. 5 shows an individual of 

 this kind two weeks after the operation, a time when atrophy has 

 already begun in cases of operation distal to the ostia. In my 

 experiments a considerable number of these cases were kept for 

 four and a half months. During this time decrease in size of 

 the whole body occurred since the animals were not fed and in 

 most cases both the oral and aboral tentacles of the region distal 

 to the incision became somewhat shorter than the others, though 

 there was no visible atrophy such as occurs in the other cases 

 (Fig. 3). Fig. 6 shows an individual of this kind one hundred 



