MUSCLE, NERVE AND LOCOMOTION 



67 



Structures but in the dorso-ventral muscles they are frequently 

 branched at the ends, providing multiple insertions into the body 

 wall. The nucleus is usually in the central sarcoplasm but in a 

 few cases it is in a lateral protuberance of the sarcoplasm (Fig. 36c). 

 The myoplasm consists of large numbers of myofibrillae regularly 

 arranged and separated one from the other by thin lamellae of 

 sarcoplasm (Fig. 36a). In Haemopis longitudinal muscle cells are 



(0) 



(b) 



(0 



(d) 



20/^ 



Tendon 



Epidermal eel 



Cuticle 



Muscle cell 



Fig. 36. (a) and (b) transverse and longitudinal sections of part 



of a normal muscle fibre ; (c) and (d) sections showing how the 



sarcoplasm may form a lateral protuberance ; (e) the attachment 



of a muscle to the cuticle, after Sukatschoff, 1912. 



5-15 mm long when moderately contracted (Schwab, 1949). In a 

 nerve-muscle preparation contraction may be initiated by electrical 

 stimulation of the nerve or muscle or by immersion in a dilute 

 solution of acetylcholine. The latter reaction has been used as a 

 test for the presence of acetylcholine (Minz, 1932) as contractions 

 are produced with concentrations as low as 1 X 10~^. Eserine 

 increases the response to a given stimulus, but curare inhibits it. 

 It has recently been found that morphine in the appropriate 



