REGULATION OF HARENACTIS ATTENUATA. I I 



of extending sufficiently to insert the aboral end in the sand, or 

 else they have lost their earlier method of reaction. Whichever 

 the case, animals like Figs. 13-16 have never been observed to 

 enter the sand and resume their original habit, after being placed 

 on the surface of sand or even being imbedded in it. In the 

 latter case they usually work their way out of the sand in a few 

 hours and lie on its surface. It seems probable, however, that 

 if they could be kept imbedded in the sand for a considerable 

 length of time, more or less, perhaps complete return to the 

 original form and habit might occur. Further experiment is 

 necessary to determine this point. 



3. The " Foot" of Harenactis. 



In the figures showing the foot, the region actually attached to 

 the substratum is indicated by a heavier line. As the figures show 

 at once, this region is extremely variable in extent : in Figs. 5 

 and 6 there is no distinct region of attachment, in Figs, i 

 and 2 the region of attachment is a very small area, in Figs. 3 

 and 4 it is somewhat larger, in Figs. 10 and 12 it is a disc almost 

 equal in diameter to the other regions of the column, and finally 

 in Fig. 1 6 its diameter is much greater than that of any other 

 part of the body. In Figs. 14 and 15 only a small part of the 

 flattened aboral surface is attached, the region of attachment 

 being in the one case in the middle and in the other on the 

 margin. In Fig. 13 there is no trace of an adhesive region, and 

 individuals of this sort which have been unattached during sev- 

 eral weeks appear to be unable to attach themselves again, even 

 if placed with the aboral end in contact, though it is probable 

 that they might again acquire the power of attachment after a 

 time. 



The foot-region is not markedly different anatomically from the 

 other parts of the body-wall. When an attached region is freed 

 and examined it usually appears somewhat more transparent than 

 other regions, but otherwise essentially similar to them. Never- 

 theless the region of the body within which attachment may occur 

 is more or less sharply limited. Individuals which lie on their 

 sides in the dishes do not become attached unless the region in 

 contact with the dish is near the aboral end, in which case they 

 may sometimes attach themselves. 



