10 



ELECTRO-PHYSIOLOGY 



CHAP. 



Hydra, furnished with a fiagellum, also possess basal muscular 

 fibrils. A similar but more complicated arrangement exists in 

 the Actinia. We are still in every case dealing with muscles of 

 epithelial origin, epithelial muscle-cells, which take part in the 

 external or internal limitation of the body- surface, or lie deep 

 down their epithelial origin being always, however, unmistakable. 

 In the simplest case, a transverse section through the endoderm 

 shows, as in Hydra, a single row of shining granules, lying under 

 a single layer of cylindrical, epithelial cells, which it divides from 

 the mesenchyme (Fig. 2, a). 



Here again, as we learn from isolated preparations, we have 

 a cross-section of muscle-fibrils (bundles 

 of fibrils ?) which must be regarded as 

 a differentiation product of the epi- 

 thelial cells. The cell-bodies are cubical, 

 cylindrical, or filiform, according to 

 the state of contraction of the body- 

 wall ; they carry cilia, or a solitary 

 flagellum, at their free ends, while 

 muscle-fibrils are differentiated off at 

 the base, which is somewhat broader 

 (Fig. 2, 5). From this primitive form 

 it is easy to derive what Hertwig (9) 



FIG. 2. a, Transverse section through Calls " intra - epithelial " niUSCleS, ill 



which the ^die-shaped cell-bodies 



to the long axis of the basai are only interspersed between the epi- 



fibrils ; b. epithelial muscle -cell .1 > > TI -, , -, , 



(isolated) of Actinia. (Hertwig.) thelial cells proper, and take no part in 

 bounding the upper surface. The " sub- 

 epithelial " muscles are directly connected with these forms ; they 

 consist of long fine bands (bundles of fibrils), which only retain 

 a thin sheet of formative plasma on the side nearest to the 

 epithelium. 



There can be no doubt that the nucleated mass of protoplasm 

 here corresponds with the body of a genuine epithelial muscle-cell. 

 There is merely a structural difference between the last-named 

 muscles and those bundles of muscle-fibrils which are completely 

 surrounded by mesenchyme, and are derived from a corresponding 

 number of myoblasts. 



. The individual elements in this case also are fibres (fibrils), 

 with plasma and nucleus ; but instead of lying in single juxta- 



