OPALINA. VOKTICELLA 7 



III. OPALINA. 



Opalina is a protozoon usually found living in large 

 numbers in the large intestine of the frog. From its large 

 size and the ease and certainty with which it can be obtained 

 it is a very convenient form for examination. 



Slit up the large intestine of a freshly -pithed frog ; remove 

 the contents and dilute them with salt solution ('75 per cent.). 

 Examine a drop of the mixture microscopically. 



A. General appearance. 



Opalina is a flattened, asymmetrically oval body, about 

 ^3- inch long, covered with cilia by means of which it swims 

 actively. It has neither mouth nor anus. 



B. Structure. 



1. The ectosarc is thinner than in Paramecium. There 



are no pulsating vacuoles, and no trichocysts. 



a. The cuticle, if present at all, is exceedingly thin. 



b. The cilia are of equal size over the whole surface. 



c. ' Myophan ' striations are obvious : they are mainly 



longitudinal. 



2. The endosarc contains no food-vacuoles, owing to the 



fluid nature of the food : this also accounts for the 

 absence of a mouth, the nutriment being absorbed 

 by the whole surface of the cell -body. 



a, The nuclei are numerous. 



C. Reproduction. 



This is effected by oblique or transverse fission. 



IV. VOETICELLA. 



Vorticella, which is just recognisable with the naked eye, 

 differs from the two preceding infusorians in being attached 

 by a contractile stalk to plants or other objects, often to other 

 aquatic animals ; it may, however, under certain conditions 

 become detached from its stalk and swim freely. 



