SECTION THROUGH BUCCAL CAVITY. 199 



b. The dermis is a very thin layer of connective tissue 

 underlying and supporting the epidermis. 



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 occupying the 

 vacuoles of the notochordal cells, the outlines of 

 which are indicated by the wavy bands. 



Near the surface of the notochord, and espe- 

 cially in the dorsal region, cells maybe 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 outwards 

 to form the septa : these latter separate the myo- 

 tomes from one another, and are continuous at 

 their 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 reagents. 



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. 



