ELEMENTARY VITAL PHENOMENA 



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muscle-fibrillce ; the fibrillge lie embedded in the protoplasm 

 of the fibre, which can be termed with Rollett, in brief, sarco- 

 plasm, arranged in various ways but all in the same direction. 

 They represent specially differentiated organoids of the cell- 

 protoplasm. 



In accordance with the varying structure of the contractile 

 muscle-fibrillaB, two groups of muscle-fibres or muscle-cells are 

 distinguished, the smooth and the cross-striated. In smooth 

 muscle-fibres the fibrillas, which lie embedded in the sarcoplasm 

 parallel to one another, are completely homogeneous threads in 



A B C 



FIG. 100. Stentor cceruleus, a ciliate infusorian containing numerous parallel muscle-fibrillfe 

 (myoid-fibres) in the exoplasm. A, Extended ; B, half -contracted (free-swimming) ; C, 

 wholly contracted. 



which every cross-section is like every other one. Cross-striated 

 muscle-fibres, on the other hand, contain fibrillge that from one 

 end to the other are divided into many segments, all of which 

 possess a corresponding but complicated structure. 



The simplest forms of smooth muscle-cells are found among 

 Infusoria. In many ciliate Infusoria, such as Stentor, the cell-body 

 represents such a muscle-cell of the simplest kind ; it contains, 

 embedded in the external layer of its protoplasm, smooth 

 muscle-fibrillse, the so-called myoids, arranged approximately 

 parallel to one another (Fig. 100). Other Infusoria, especially 



