26 MORPHOLOGY OF INVERTEBRATE TYPES 



with the shelf to which the polyps are attached, the perisarc, 

 the hydrothecae with their terminal aperture and two-flapped 

 operculum, the diaphragm at the base of the hydrotheca, the 

 hydranths with the single circle of filiform tentacles, hypostome, 

 mouth and ectodermal fold serving as protractor. 



3. Examine in the same manner a gonosome. Make a half 

 page drawing of two internodes of the stem carrying the gonan- 

 gium, the blastostyle, gonophore and gubernacula or strands 

 representing the remains of the previous gonophore which had 

 been emptied. 



4. Examine in the same way the terminal bud (200 diameters) 

 and make a drawing of it. 



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

 slide with a stained colony and make a drawing of a tentacle 

 showing its structure. 



6. Examine under high power (400 diameters) the cross-sec- 

 tion through a hydranth and make a drawing showing hy- 

 drotheca, ectodermal fold, ectoderm, mesoglcea, endoderm and 

 ccelenteron. 



7. Additional exercise. Find among the colonies a gonosome 

 in which an acrocyst has been formed above the gonangium. 

 Cut it off with a piece of the stem, place on a slide in a drop of 

 glycerine, cover with a cover glass and examine under low power 

 (50 diameters). Make a drawing showing details 



