32 Laboratory Guide in Zoology 



IV. — Learn whether the Rotifer revolves frequently on its 

 longitudinal axis. Do you conclude that the animal 

 has a dorsal and a ventral surface .'' 



V. — The cause of the free-swimming movement will be 



easily made out. Notice that the head appears as if a 

 revolving wheel were attached to its surface : in many 

 species there are two disks showing this motion. This 

 appearance is caused by the rhythmical motion of one 

 or two bands of cilia encircling the disks of the head. 

 These revolving cilia form one means of locomotion. 

 Notice how the contraction of the body affects its 

 movement. 



VI. — Study the hard, vase-shaped case into which the 

 extremities of the body are drawn. Observe the 

 degree of its flexibility as the Rotifer moves about. 

 This case is called the lorica; in it are crowded the 

 organs for ingesting, masticating, digesting, and assimi- 

 lating food, and for egesting waste material ; also the 

 organs of reproduction. 



VII. — Watch again the head and foot as they are drawn 

 in, and notice that it is then much more difficult to 

 distinguish the parts inside. Observe the Rotifer as it 

 stretches out; you will be able to see narrow bands 

 passing along the body beneath the lorica. Similar 

 bands encircle the body. These two sets form the 

 muscular system of the Rotifer : the movements of the 

 body are due to the contractile power of the muscles. 



VIII. — Add a few grains of powdered carmine to the water 

 on the slide. When the particles come near an active 

 Rotifer, see the vortex caused by the movements of the 

 cilia. Watch for the swallowing of some of these 

 grains when the head is suddenly drawn into the body. 

 When two disks of cilia appear, the mouth may be seen 



