REGULATION OF HARENACT1S ATTENUATA. 



many of these individuals have completely lost the power of at- 

 taching themselves, though it is possible that the sac-like form of 

 the body is responsible for their failure to attach, since the aboral 

 region usually does not come into contact with the substratum. 

 Figs. 14 and 15 show other cases, in which the decrease in 

 length is still greater, but in which the aboral end is more flat- 

 tened and still retains the power of attachment. These cases 

 illustrate the conditions usually found when the attachment to the 



FIGS. 13-16. 



Although a flattened 



substratum is less frequently disturbed, 

 aboral region of greater diameter than any other part of the body 

 is present, attachment does not always occur over the whole sur- 

 face ; apparently, however, any part of the surface is capable of 

 serving as the organ of attachment, the animals being attached 

 in some cases by a small region in the middle of the flattened 

 surface (Fig. .15), and in other cases by some part or parts of its 

 margin (Fig. 14). In fact the region of actual attachment may 

 differ at different times in the same individual. 



