12 



ELECTRO-PHYSIOLOGY 



CHAP. 



with a row of fibrils lying one behind the other dotted in trans- 

 verse section (Fig. 4, B). 



The relative disposition of the contractile layer and formative 

 plasma (sarcoplasm) varies considerably in different muscles of 

 worms. In the simplest case each muscle is represented by an 

 even lamina, capped by the nucleated protoplasm (Fig. 4, JB). 

 It is evident that this arrangement, in which the longitudinal 

 muscular fibrils collectively form a cylindrical surface, underlying 

 the hypodermis, corresponds with the smooth, simple, non-voluted 

 muscular lamella of many Cnidaria. In both cases increase of 

 mass in the contractile substance leads to a formation of folds, 

 which in Nematode muscles may be detected in each single cell. 

 The fibrillar layer, at first a level surface, curves into a hollow 

 groove, opening into the ccelom, and filled with formative plasma. 



FIG. 4. A, Branchiobdella pamsitica ; transverse section through the muscles of the body-wall. 

 a, coelomyoid ; b, holomyoid muscle-cells. B, Section through a platymyoid muscle-cell of 

 Ascaris lumbricoides. (Rhode.) 



Ehode (8), e.g., finds in the longitudinal muscle-layer of Branchio- 

 bdella parasitica, every conceivable form of transition between the 

 "platymyoid" type of muscle-cells described above, in which the 

 fibrillated contractile stratum forms an even lamina, and the 

 " ccdomyoid " type, where the fibrillar layer has become grooved 

 (Fig. 4, A, a). 



And, again, there is but a step from these to the closed tubular 

 muscle-cells, in which the plasma forms an axial filament sheathed 

 on all sides by the contractile fibres. 



The longitudinal fibres of the sheath of the cutaneous muscle 

 of Ascaris are among the most interesting of the ccelomyoid 

 muscle-cells. Here the sarcoplasm is already walled in by the 

 contractile substance at the ends of many of the muscle-cells, 

 while in the centre the nucleated plasma (surrounded by a 

 sarcolemma) bulges out like a hernial sac, and is often of gigantic 



