REGULATION OF HARENACTIS ATTENUATA. 



5 



brought into a vessel without sand. Afterward it may become 

 attached to the side or bottom of the vessel or may remain unat- 

 tached. Very commonly when the foot is free, the aboral end 

 of the body takes the shape of Fig. 8, though forms like Fig. 9 

 often appear. In some cases the attenuated posterior region is 

 entirely absent and the animal is attached by a disc of nearly the 

 same diameter as other parts of the body (Fig. 10), or the aboral 

 end may be free and rounded. These various shapes are merely 

 the visible expression of various states of contraction or extension 

 and change more or less widely in the individual. The most in- 

 teresting feature is that the body outside of its burrow never in 

 any case, so far as my observations go, extends as completely as 

 in the burrow. 



8 



IO 



FIGS. 8-10. 



The animals in water without sand very commonly exhibit 

 negative geotaxis in some slight degree, though never as strongly 

 as Ceriantkns (Loeb, '91 ; Child, '03, p. 243). No matter how 

 firmly the foot may be attached to the substratum, the animal is 



