CH. VI.] 



VOLUNTARY MUSCLE. 



have protoplasm composed of two materials, spongioplasm and 

 hyaloplasm. In amreboid movement the irregular arrangement of 

 the spongioplasm allows the hyaloplasm to flow in and out of it 

 in any direction. In ciliary movement the flow is limited by the 

 arrangement of the spongioplasm to one direction ; hence the 



Fig. 1 10. Wave of contraction parsing 'over a muscular fibre of water-beetle. R, R, por- 

 tion* of the flbie at rest ; c, contracted part ; i, i, intei mediate condition. (Schafer.) 



limitation of the movement in one direction (see p. 33). In 

 muscle, also, the definite arrangement of the spongioplasm (repre- 

 sented by the sarcous element) in a longitudinal direction directs 

 the movement of the hyaloplasm (represented by the clear sub- 

 stance of the light stripe), so that it must flow either in or out in 

 that particular direction. The muscular fibre is made up of 

 sarcostylcs and the sarcostylc of sarcomeres. The contraction of 



