96 C. F. MARSHALL. 



changes during contraction. He states 1 from observations on 

 the living fibre that during contraction his " muscle-rods " 

 (which correspond to the longitudinal bars of the network) 

 become compressed in the centre and their substance tends to 

 accumulate towards the ends, i. e. that the knotted ends of the 

 muscle-rods, which correspond to the nodal points of the net- 

 work, increase in size at the expense of the shafts connecting 

 them. On examination of the living fibre this certainly appears 

 to be the case, but the optical effects of reflection and refrac- 

 tion are so great as to obscure the real change that takes 

 place. 



Nature and Function of the Network. 



In discussing the theory of contraction, I shall assume that 

 the intracellular network of striped muscle, and the longitu- 

 dinal fibrils of the vertebrate unstriped muscle, are of 

 the same nature as other intracellular networks; and, in 

 accordance with the views of modern histologists, that they 

 are protoplasmic in nature, and denser than the rest of the 

 cell. 



We have first to consider the nature of intracellular net- 

 works in general, and whether the function is an active or a 

 passive one. In the case of intranuclear networks the changes 

 which the network undergoes in karyokinetic division of the 

 nucleus point to their being of an active nature. The extra- 

 nuclear network (intracellular) is apparently of the same 

 nature as the intranuclear, since the two have been shown to 

 be continuous in many cells ; and also they have the same 

 behaviour towards stains and reagents. Moreover, if intra- 

 cellular networks are developed by a process of vacuolation of 

 the protoplasm of the cell, or a division into denser and less 

 dense parts, as described previously when treating of the Pro- 

 tozoa, it is obvious that in these cases the network must be 

 the active and the contractile part of the cell. 



1 "On the Leg-muscles of the Water-beetle," 'Phil. Trans./ 1873. 



