50 



C. M. CHILD. 



On the other hand, the body-wall of this species is incapable 

 of supporting alone the pressure of the enteric fluid. Under 

 normal conditions the body-wall is supported by the wall of the 

 burrow in which the animal lives and so does not support the 

 entire pressure. When the animals are kept without sand in 



y 



24 



which to burrow the shape of the body undergoes marked changes, 

 especially at the aboral end, where the wall is thinnest. Under 

 these conditions the aboral region of the body gradually increases 

 in diameter and decreases in length (Fig. 22) and the change 

 involves more and more of the body (Fig. 23), until in some cases 

 almost the whole body aboral to the oesophagus approaches a 



