178 THE ELEMENTARY NERVOUS SYSTEM 



sists of a sheet of fibers applied to the entodennic face 

 of the supporting lamella and extending at right angles 

 to those of the longitudinal muscle. Near the distal end 

 of the stalk there is usually a marked constriction, which 

 is apparently brought about by the excessive contraction 

 of the circular muscle fibers of that region. This con- 

 striction suggests the presence of a specialized muscular 

 sphincter, such as has been claimed by Riddle (1911) in 

 Tubular la, but, as a special accumulation of fibers in this 

 region appears not to be present, it seems scarcely ap- 

 propriate to describe a sphincter muscle as distinct from 

 the rest of the circular muscle of the stalk. 



An ectodermic longitudinal muscle and an entoder- 

 mic circular one occur in the proboscis exactly as they 

 do in the stalk. In sections of both the proximal and dis- 

 tal tentacles longitudinal ectodermic muscles can be seen. 

 The circular entodermic muscles mentioned by Torrey 

 (1904 b) as present in the two sets of tentacles, have not 

 been identified. If they are present, they must be rela- 

 tively poorly developed, for, in material in which the 

 longitudinal fibers could be clearly demonstrated, the cir- 

 cular fibers could not be seen, though the plane of sec- 

 tion was entirely favorable for this purpose. Cory- 

 morpha, therefore, possesses at most only six muscles 

 or groups of muscles: (1) the longitudinal muscle of the 

 stalk, (2) the circular muscle of the stalk, (3) the longi- 

 tudinal muscle of the proboscis, (4) the circular muscle 

 of the proboscis, (5) the longitudinal muscles of the prox- 

 imal tentacles, and (6) the longitudinal muscles of the 

 distal tentacles. This enumeration does not include the 

 longitudinal muscles of the peduncles of the sessile me- 

 dusae nor those of the medusa? themselves, whose activity, 

 as Torrey (1907) has pointed out, implies the presence of 



