ECHINODERMATA. 



173 



Fig. 73. 



bands running in different directions, which by their contraction 

 give rise to the various movements of the creature ; of these muscle 

 five strong fasciculi 

 assume a longitu- 

 dinal course, pass- 

 ing along the entire 

 length of the ani- 

 mal from the mouth 

 to the cloaca, and 

 in the interspaces 

 between these cir- 

 cular and oblique 

 muscles are readi- 

 ly distinguishable. 

 The whole of this 

 muscular case is 

 lined with a deli- 

 cate membrane or 

 peritoneum, from 

 which processes 

 pass inwards, to 

 support the various 

 viscera. 



(214.) But al- 

 though the calca- 

 reous shell of the 

 Echinus is thus to- 

 tally lost, the lo- 

 comotive suckers or 

 feet already de- 

 scribed are still 

 the principal agents employed in progression. In many species, 

 as in that represented in the annexed figure, (Jig. 73,) these organs 

 are distributed over the whole surface of the animal, and are pro- 

 truded through countless minute orifices which perforate the in- 

 tegument. In other cases, as in H. frondosa, they are arranged 

 in five series, resembling the ambulacra of an Echinus ; and in some 

 instances they are only found upon the middle of the ventral sur- 

 face of the body, that forms a flattened disc upon which the ani- 

 mal creeps, somewhat in the manner of a snail. The ambulacral 

 feet themselves, represented on an enlarged scale at (c), pre- 



