ORGANISATION AND STRUCTURE OF MUSCLE 



18 



proportions in comparison with the fibrillar stratum (Fig. 5, 

 A, B). A transverse section through the centre of such a cell 



FIG. 5. A, Section through part of the muscular layer of 

 Ascaris lumbricoides ; a, vesicular swellings of sarco- 

 plasm ; /3, contractile substance ; y, cell-nucleus. (R. 

 Leukart.) B, Isolated muscle-cells of Ascaris, from the 

 Eel. (Hertwig.) 



shows the contractile substance in a horse-shoe 

 figure, with the sarcoplasm rising within it ; near 

 the ends of the fibres only a ring of contractile 

 substance, enclosing a cleft filled with proto- 

 plasm, is exhibited. In many cases the similarity 

 of arrangement, in transverse section, of the 

 fibrils of the longitudinal muscular layer of 

 worms, and the involuted muscle - lamella of 

 certain cnidarians, is very striking. 



The muscle-cells of most other worms agree 

 in their finer structure with the forms described, 

 being either of a fiat, a hollow, or more frequently 

 a tubular type. The only differences are in 

 the size and arrangement of the separate 

 elements, and also in the comparative develop- 

 ment of volume of the sarcoplasm and con- 

 tractile substance. The fibrillated structure of the contractile 

 tissue is not always easy to distinguish, but cf. Ehode (I.e.) on 

 the musculature of Chsetopoda appears to be very generally 



