IO C. M. CHILD. 



The form that is in some respects of greatest interest is shown 

 in Fig. 1 6. In such cases the body is usually attached over more 

 or less of the flattened aboral surface, though occasionally such 

 forms appear without actual attachment, provided the body is 

 broad enough to stand upright on its aboral end. Apparently the 

 mere contact without attachment is sufficient to bring about more 

 or less flattening of the aboral end. In these flattened forms the 

 power of invagination of the oral end is almost entirely absent. 

 Violent stimulation may bring about a slight temporary increase 

 in the flattening, with perhaps some depression of the oral region 

 which does not amount to actual invagination. 



The interesting feature in these cases is that the originally 

 greatly elongated, attenuated body has acquired a form almost 

 exactly similar to that of those actinians which are normally sessile 

 on the surfaces of rocks, etc. The ability to retract the oral end has 

 been almost or wholly lost, but from certain observations toward 

 the conclusion of my experiments, it seems not impossible that in 

 the further course of regulation this power may be regained to a 

 greater or less extent. These observations were simply that 

 many individuals seemed to possess a greater power of retraction 

 of the oral end after four and a half than after three and a half 

 months. If this difference is real it may be due either to the 

 regulation of the longitudinal muscles so that further contraction 

 is possible, or to regulatory decrease in the bulk of mesenteries, 

 filaments, etc., or to both factors. The volume of the retractor 

 muscles very evidently decreases during the regulation, and 

 it is extremely probable that the other parts, being folded and 

 packed together so much more closely than originally, undergo 

 more or less atrophy. In short, it appears almost certain, though 

 the length of time covered by my experiments is insufficient for 

 a demonstration, that Harenactis attcmtata may, in altered envi- 

 ronment, acquire most of the characteristics of those actinians 

 which are normally sessile on surfaces exposed to the water. 



Individuals removed from their burrows and placed upon the 

 surface of the sand usually succeed in working their way back 

 into it by means of the attenuated aboral end which acquires the 

 form of Fig. 6 under these conditions. After the regulation 

 has occurred, however, they appear to be absolutely incapable 



