500 C. M. Child 



In the other two cases described only three tentacles were 

 entirely absent, but a number of others in irregularly arranged 

 groups about the margin of the disc appeared later and were for 

 a long time much smaller than the remainder (Fig. 24). In these 

 cases no definite relations exist between the mesenterial arrange- 

 ment and the regions where tentacles are lost or reduced in size. 



In my work on Cerianthus I showed that local inhibition of 

 tentacle-formation might occur as the result of folds in the body- 

 wall (Child '04b, pp. 281-284). If these folds persist for any 

 considerable length of time atrophy of the region occurs. This is 

 especially noticeable in Cerianthus aestuarii (Child '08) where 

 complete degeneration and disintegration of the body-wall in 

 folds and compressed regions often occurs. 



The reason for this local atrophy in folded or wrinkled regions 

 lies in the fact that even in "collapsed" pieces, i.e., in pieces with 

 an artificial opening into the enteron which prevents normal dis- 

 tension, some slight degree of distension exists so long as the pieces 

 are undisturbed (Child '04b, '04c, etc.). In Cerianthus the 

 wound becomes plugged by the slime secretion, in Harenactis by 

 slime and in certain regions by the cut ends of muscles and mesen- 

 teries. Consequently some degree of distension arises, as can 

 easily be shown experimentally, but the pressure cannot attain 

 anything like that in normal animals for as soon as it exceeds a 

 certain small amount water escapes through the wound. Such 

 slight distension is not sufficient to remove the folds and wrinkles 

 from the body-wall, and these regions are consequently not sub- 

 jected even to the slight degree of tension existing elsewhere, 

 therefore they undergo more reduction or atrophy than the other 

 regions. Experimental demonstration of these facts is not in the 

 least difficult. I have observed and established experimentally 

 these conditions in a very large number of cases, especially in 

 Cerianthus aestuarii. 



The two pieces of Harenactis are simply further examples of 

 local inhibition of tentacle-formation in consequence of local 

 atrophy. Since closure is retarded in these pieces they remain 

 collapsed for a much longer time than is usual in more distal pieces, 

 and during the period of collapse the body becomes variously 



