22 STUDIES OF ANIMAL TYPES 



a system of radial canals that run nearly through the walls 

 of the body, but end blindly just before reaching the out- 

 side. Make a very thin, longitudinal section with a razor 

 and examine with the microscope. Note these radial canals 

 and also a set of parallel canals that begin at the outside 

 of the body and end blindly just before reaching the 

 body cavity. The radial and inhalent canals communicate 

 with each other by fine openings through their adjoining 

 walls. 



Draw one half of the sponge (enlarged) to show the 

 body cavity and the radial canals. 



Make a very thin cross section of a dry sponge. Note 

 the round opening in the center of the section. What is 

 this ? Note the two sets of canals mentioned above. Note 

 the arrangement of 'the spicules in the walls of these 

 canals. 



Boil a small piece of the sponge for a short time in caus- 

 tic soda, in a test tube. The spicules will separate from 

 the tissues and fall to the bottom. Mount some of them on 

 a slide. At least two kinds will be found, the tri-radiate 

 and the needle-shaped. The tri-radiate spicules, will, 

 for the most part, have the "prongs running off at equal 

 angles of 120 from each other. Occasionally some will 

 be found in which the prongs form right angles. In this 

 case the spicules are T-shaped. 



Make drawings of the different kinds of spicules. 



C. TOPICS FOR FURTHER STUDY. Sum up the leading 

 characteristics of a simple sponge. To what branch does 

 it belong ? Compare it with an amoeba. Discuss its man- 

 ner of obtaining food. How does it reproduce? How 

 does it respire ? Where is it found ? Note that it is a 

 multicellular animal, but stands next 'to the Protozoa. 



