OPALINA. 7 



united by their ventral surfaces, and, after swim- 

 ming about together for some time, separate 

 and become independent again. During and 

 after this union certain changes occur in the 

 nuclei and paranuclei of both individuals, result- 

 ing in the so-called ' rejuvenescence,' and 

 followed by rapid and repeated fission of the 

 two Paramecia. 



Kill the Paramecia by running a drop of acetic acid (1 

 per cent^ under the cover-glass ; and then stain with dahlia 

 or carmine. 



The nucleus and the discharged trichocysts are well seen 

 in specimens so treated. 



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 ; scrape 

 away the contents together ivith the epithelial lining of the 

 intestine, and dilute loith salt solution (-75 per cent.). 

 Examine a drop of the mixture microscopically. 



A. General appearance. 



Opalina is a flattened, asymmetrically oval body, about 

 1 



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. 



g-s inch long, covered with cilia by means of which it swims 



