12 C. M. CHILD. 



We may conclude then that a more or less well defined aboral 

 region of the body is usually capable of reacting to contact with 

 solid objects by adhesion. Only those parts of this surface which 

 are or have very lately been in actual contact are adhesive at any 

 given time. 



But the limits of the region within which reaction to contact by 

 adhesion is possible may vary very considerably, as the obser- 

 vations above cited show. At the time of removal from the 

 natural habitat the region of attachment is always limited, so far 

 as my observations on several hundred individuals go, to a rela- 

 tively very small area at the aboral end (Figs. 1-4). Sometimes 

 after a day or two in the laboratory animals are found attached 

 by a considerably broader area (Fig. 10), but I have never seen 

 the slightest indication that regions still farther from the aboral 

 pole possessed at this time the power to react in this manner, 

 though I have often observed animals with these regions in con- 

 tact. But after several months in shallow water without sand in- 

 dividuals like Figs. 14, 15 and 16 are of frequent occurrence. In 

 these any portion of the broad flattened aboral region is capable 

 of reacting to contact by adhesion and sometimes, as in Fig. 16, 

 the whole region is involved . In Fig. 16 the radius of this foot- 

 region is almost equal to the length of the column oral to it : if 

 all parts of the body-wall have undergone atrophy in equal de- 

 gree then the foot-region as shown in Fig. 16 consists of what 

 was originally the aboral half more or less of the column. It is 

 of course impossible to determine whether all parts of the body- 

 wall have undergone atrophy in equal degree, but that point 

 aside, it is sufficiently evident that the extent of the foot-region 

 is very different in Figs. I and 16. If the regions of the body 

 oral to the small disc of attachment in Fig. I were definitely 

 specified as regions capable of attachment, we should expect to 

 find objects adhering to them, at least occasionally, for they fre- 

 quently come into contact with solid objects in the walls of the 

 burrow. In some cases I have observed objects adhering to the 

 oral as well as to the aboral surface of the disc of attachment, but 

 never to regions oral to this. 



In short the differences in extent of the foot-region in extreme 

 cases like Figs. I and 16 show that the extent of the region 



