

SECTION THROUGH BUCCAL CAVITY. 207 



3. The skeletal system. 



a. The notochord is oval in section, the longer axis 



being vertical. It is crossed by numerous wavy 

 transverse bands, the spaces between which are 

 occupied by a homogeneous substance : this 

 latter is the coagulated semifluid matter occupy- 

 ing the vacuoles of the notochordal cells, the 

 outlines of which are indicated by the wavy 

 bands. 



Near the surface of the notochord, and 

 especially in the dorsal region, cells may be 

 seen which have undergone comparatively little 

 modification. 



b. The connective tissue forms a thick deeply staining 



investment to the notochord, which is prolonged 

 upwards to enclose the spinal cord, and out- 

 wards to form the septa : these latter separate 

 the myotomes from each other, and are con- 

 tinuous at the outer borders with the dermis. 



c. The buccal skeleton. Sections of the segmented 



rods which strengthen the lips are seen bordering 

 the entrance to the buccal cavity : a smaller rod 

 occupies the axis of each tentacle. In structure 

 these rods resemble the notochord. 



d. The skeleton of the dorsal fin. The dorsal fin is 



filled with a homogeneous gelatinous substance, 

 which is stained slightly by re-agents. 



4. The muscles. 



a. The myotomes are seen in section as squarish 

 masses of muscle lying along the sides of the 

 body in the compartments formed by the septa. 

 Owing to the obliquity of the myotomes, three 

 or more are cut in each transverse section, and 

 owing to their > shape each myotome is cut 

 twice. The myotomes of the two sides are not 

 opposite, but alternate with each other. 



