THE MUSCULAR SYSTEM. 187 



case. The course of this thread is indicated by the 

 dotted line in fig. 4. 



These threads tie the stomach to one position in 

 the cell ; but besides these there is another thread, 

 which is fastened to the hinder part of this viscus, and 

 passes down diagonally to the hinder part of the cell, 

 where it is inserted in the walls. Thus the only 

 motion permitted to the stomach is, that it may swing 

 a little backward by the elasticity of the connecting 

 threads, and this is allowed, to make room for the 

 anterior parts to retire within the cell. These, for- 

 cibly retracted by muscles presently to be described, 

 push the first stomach, and in a less degree, the 

 second also, out of the centre, towards or even into 

 contact with, the hinder wall of the cell : as it is seen 

 in Fig. 3. 



Many bands of muscular fibre appear with beauti- 

 ful distinctness in this zoophyte. The great retractor 

 muscle runs along the whole length of the animal on 

 the ventral or front surface. It is inserted into the 

 front side of the tubular foot of the cell, a good way 

 below the bottom of the cavity, through which it must 

 pass, and which therefore must be perforated near its 

 front margin as well as in the centre. The muscle 

 is a ribbon of fibres, which widen and diverge as they 

 proceed, so as to be narrowly fan-shaped ; the broad 

 end is fastened into the body of the animal, probably at 

 one or other of the points where the integument sheaths, 

 but I have not been able to trace it much beyond the 

 margin of the cell in the extruded animal. It is 

 certainly free for the greater part of its length, for I 

 have seen it, in partial retractation, thrown into sinu- 



