SMOOTH MUSCLE 99 



A sarcolemma has not been demonstrated. Its presence in this 

 muscle would demonstrate the presence of a real sarcolemma on a 

 muscle cell on account of the small amount of connective tissue in the 

 organs of the earthworm. A notable feature of this cell is the series 

 of fine fibrils that are given off from its body to connect it with the other 

 similar muscle cells with which it is in contact. These connections must 



fi 



FIG. 96. End of a single muscle fiber from the gizzard of Allolobophora. Teased preparation. 

 gr.cyt., granular cytoplasm; nu., nucleus; conn.fi., connecting fibrils broken by testing; 

 fi., muscle fibrils. X 435. 



be of considerable strength, as the muscle could not hold together and 

 operate if they were not. 



These intercellular connecting fibrils are a part and product of the 

 muscle cell, and we may say that this cell forms and uses both myo-fibrils 

 and connective-tissue fibrils. They are placed in short rows and appear 

 to emerge from the body of the cell between the myo-fibrils. Seen with 

 a lower power, they lead one to think that the muscle cell is a striated 

 one. They are broken off a short distance from the surface of a macer- 

 ated fiber where the neighboring fiber was torn away. Their presence, 

 under the high power, gives the whole cell a rough or prickly appearance. 



Such structures do not represent any vital connection between the 

 cells, not being protoplasmic in nature. They cannot, therefore, be 

 called "protoplasmic bridges," and should not be called intercellular 

 bridges, as that has come to mean the same thing. 



The muscle fibers of the squid should be briefly compared with the 

 one we have just examined. This muscle cell is of extreme length and 

 is attached, where it meets with a surface, by a blunt end; or where it 

 is interlaced with other fibers, by a long, thin ending. Its myo-fibrils 

 are massed on the surface of the fiber in a thin layer, thus leaving a 

 large cavity in which the watery sarcoplasm lies. 



The nucleus occupies the central part of this cavity, and is enormous 

 compared with the nucleus of the earthworm's gizzard cell. It makes 

 a beautiful object for the study of the nuclear organs. Figure 97 shows 

 several transverse sections and a longitudinal section of such fibers in the 

 squid's arm. 



The powerful closing muscles of the plecypod mollusks show a fiber 



