22 MORPHOLOGY OF INVERTEBRATE TYPES 



hydranth label mouth, hypostome, oral tentacles, basal ten- 

 tacles and medusa buds. 



3. Examine under high power (400 diameters) a prepared 

 slide of a polyp and make a drawing showing an oral tentacle 

 with the knob of nematocysts at the end. Label supporting 

 endoderm, mesoglcea and ectoderm. 



4. Examine on the same slide a basal tentacle and make a 

 drawing of it showing the swellings containing the batteries 

 of nematocysts, supporting endoderm and ectoderm. 



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

 slide with a cross-section through a hydranth. Make a drawing 

 showing ectoderm, mesoglcea and endoderm. 



6. Examine in the same manner the cross-section through the 

 hydrocaulus; make a drawing and label it. 



7. Place a medusa in a Syracuse dish with water under the 

 dissecting microscope. Make a quarter page drawing showing 

 the side view of the medusa. Label exumbrella, subumbrella, 

 velum, manubrium, mouth, central gastro-vascular cavity, ra- 

 dial canals, circular canal and rudimentary tentacles, one at 

 base of each radial canal. 



8. Additional exercise. Put a live fresh-water hydra on a 

 slide in a drop of water, cover it up with a cover glass and press 

 it with the point of a needle until the animal will break up into 

 small fragments. Examine under high power and find the iso- 

 lated exploded nematocysts. Make a drawing of one of them 

 showing the structure, and label parts. 



