180 



PHYSIOLOGY 



striated, the striation being apparently due to the development of special 

 contractile fibrillse. In the slowly contracting unstriated muscle of the 

 vertebrate intestine, the longitudinal striation is with difficulty made out, 

 but as the muscle rises in the scale of efficiency, the longitudinal striation 

 becomes more apparent, and in the striated muscle of vertebrates, and still 

 more in the wonderful wing-muscles of insects, which can perform three 

 hundred complete contractions in a second, the longitudinal is associated 



FIG. 36. 



FIG. 35. 



FIG. 35. Muscle fibre of an ascaris. a, the differentiated contractile portion of the 

 cell. (After HERTWIG.) 



FIG. 36. Muscle fibres from the small intestine, showing the fine longitudinal stria- 

 tion. (SCHAFER.) 



with and often apparently subordinated to a transverse striation, due to 

 the regular segmentation of the contractile fibrillse or sarcostyles. Every 

 muscular fibre, which presents any trace of histological differentiation, may 

 be said to consist of contractile fibrillse (sarcostyles), each composed of a 

 series of contractile elements (sarcous elements or sarcomeres), and embedded 

 in a granular material known as sarcoplasm. The great divergence in the 

 aspect of muscular fibres from different parts of the animal kingdom is 



