OPALINA. 7 



Conjugation is not a mode of reproduction, and is 

 closely followed by it. Two Paramecia become 

 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 mega-nuclei 

 and micro-nuclei of both individuals, resulting in 

 the so-called ' rejuvenescence.' 

 Kill and stain the Paramecia by running a drop of methyl- 

 green in acetic acid under the cover-glass ; or fix with acetic 

 acid vapour and then stain with hcematoxylin. 



The nuclei and the discharged trichocysts are well seen 

 in specimens so treated. 



D. Encystation. 



Paramecium under adverse conditions secretes a kidney- 

 shaped cyst around itself. This is however a resting cyst only. 



III. OPALINA. 



Opalina is cne of many diverse kinds of protozoa 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 with the epithelial lining of the 

 intestine, and dilute 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 1 - 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 pellicle, if present at all, is exceedingly thin. 



