TERMINATION OF MOTOR NERVES IN INVERTEBRATA. 205 



is invested by a sarcolemma, and to which only nerves provided 

 with sheaths are distributed, does not at some point allow the 

 passage of these through the membrane. Still more strongly 

 was the hypothesis respecting the continuity of the sheath of 

 Schwann with the sarcolemma, or in other words, of the passage 

 of the nerve fibre directly into the contractile substance, advanced 

 by physiologists, thus leading the way to the establishment of 

 all that has been discovered respecting the termination of motor 

 nerves since the time of Doyere. 



We shall commence with the transversely striated muscles, 

 proceeding from the lower to the higher groups of animals, and 

 leaving on one side, for the present, the relations existing in the 

 unstriated fibres, and the still very incompletely known but 

 apparently smooth muscular fibres of the worm, and other still 

 more lowly organised Invertebrata. 



THE MODE OF TERMINATION OF THE NERVES IN INVERTEBRATA. 



The striated muscles of the Articulata consist of completely 

 closed cylindrical tubes of sarcolemma, the contents of which 

 present the well-known appearance of a stage or ladder-like 

 arrangement of superimposed disks of muscle prisms.* The 

 muscle prisms are separated from each other in the transverse 

 direction by a considerable amount, and in the longitudinal by 

 a small amount, of homogeneous fluid material. All muscles, 

 moreover, contain, besides those constituents which form the 

 really contractile substance of the muscle, still another material 

 that has some, though a less important, influence on the develop- 

 ment of force. It is generally regarded as the remains of the 

 original formative cells of the muscle, and is composed of nuclei 

 with a distinctly double-contoured membrane, and transparent 

 contents, often with nucleoli ; of vesicles of various form, without 

 definite investment ; of granules ; and lastly, of a finely granular 

 pappy mass. These masses may be very variously distributed in 



* The term " disks" was introduced into the description of muscle by Mr. 

 Bowman. The same parts were designated by Rollett "chief-substance 

 disks." The muscle prisms have been also, after Mr. Bowman, termed 

 " sarcous elements." 



B 2 



