34 MORPHOLOGY OF INVERTEBRATE TYPES 



age of the individual. There are usually from sixty to eighty 

 tentacles. 



2. Cut off a piece of the bell-margin between the radial canals, 

 put it on a slide in a drop of glycerine, exumbral side uppermost. 

 Examine through the microscope under low power (100 diam- 

 eters). Make a drawing showing the circular canal and the 

 margin of the bell with the base of several tentacles and the 

 statocysts with the single concretion in them. There are usually 

 half as many statocysts as tentacles. 



3. Cut off a piece of the velum, put it on a slide in a drop 

 of glycerine, subumbral side uppermost, cover up with a cover 

 glass and examine under high power (400 diameters). Make a 

 drawing showing the epithelial cells and circular muscle fibres. 



4. Sever a tentacle and examine in the same manner that 

 region of it where it is bent at right angles. Make a drawing 

 showing the rings of nematocysts and the cup-like adhesive pad. 



5. Examine under high power (400 diameters) the prepared 

 slide with a cross-section of a tentacle. Make a drawing 

 showing the central cavity, supporting endoderm composed of 

 large cells with small nuclei, mesoglcea and ectoderm with ovoid 

 nematocysts and muscular fibres. 



6. Examine the radial section through the edge of the bell 

 and the velum. Make a half page drawing showing the circular 

 canal, mesoglcea, ectoderm of the subumbrella, subumbral 

 ectodermal layer of the velum with the circular muscles, exum- 

 bral ectodermal layer, subumbral nervous ring and exumbral 

 nervous ring. 



7. Examine a cross section through the manubrium (50 di- 

 ameters) and make a drawing showing the cross-shaped cavity 

 of the stomach, mesoglcea and endoderm. 



