GRANTIA CILIATA FABRICIUS 15 



surface. Make a half page drawing showing the osculum with 

 its spicules, atrium, apopyks or pores in the wall of the atrium, 

 and the radial tubes and incurrent canals in the cut surface of 

 the wall. 



3. Examine under low power (50 diameters) a prepared slide 

 with a cross-section through Grantia showing the arrangement 

 of spicules. Make a half page drawing showing four of the 

 radial tubes indicated by the rows of spicules. 



4. Examine under microscope (200 diameters) a prepared 

 slide of isolated spicules. Make a drawing of a triradial spicule 

 and of shorter and longer needle-like spicules. 



5. Examine under low power (100 diameters) a stained cross- 

 section. Make a half page drawing showing four radial tubes. 

 Label external pore, incurrent canal, radial tube, and apopyle. 



6. Examine the same section under high power (400 diame- 

 ters). Find a place with an embryo. Make a drawing showing 

 the three layers of cells; label choanocytes (collar cells), ectoderm, 

 mesenchyme, and embryo. If possible, find and show on the 

 drawing a prosopyle. 



7. Examine under low power (200 diameters) a stained tan- 

 gential section. Determine which rings represent the cross- 

 sections of radial tubes by the shape of the cells facing the center 

 of the ring. In doing so, remember that the radial tubes are 

 lined with endodermic choanocytes (collar cells), while the 

 incurrent canals have flat ectodermal cells. Make a half page 

 drawing showing several of the tubes and canals and label them. 



8. Additional exercise. Boil an alcoholic specimen in a test 

 tube containing a solution of potassium hydrate. When all 

 the tissues are dissolved, allow the spicules to settle, carefully 

 pour off the liquid and wash the spicules twice in clean water. 

 Pick up a number of spicules by means of a pipette and transfer 

 them on to a slide. Place them under the microscope and focus. 

 Add now a small drop of a 10% solution of hydrochloric acid 

 and observe how the spicules dissolve with the formation of 

 small gas bubbles, proving their calcareous nature. 



