3 THE PROTOZOA. 



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 during spring and summer by oblique 

 or transverse fission. 



Kill the Opalince by running a drop of acetic acid (1 per 

 cent.) under the cover-glass ; and then stain with safranin or 

 carmine. 



D. Conjugation. 



In late summer very small opalinaG have been observed 

 to become encysted, and in this state they leave the frog and 

 are subsequently swallowed by tadpoles. Within the cyst the 

 Opalina divides into gametes. Two of these fuse, and the 

 zygote so produced becomes encysted and subsequently 

 develops into a multinucleate form. 



IV. VORTICELLA. 



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. 



Both freshwater and marine forms of Vorticella are known. 

 The following description applies more particularly to some 

 of the larger freshwater species, but most of the marine forms 

 closely resemble these. 



Vorticella may be distinguished from allied genera which 

 are often found with it by its unbranched stalk, and by the 

 spiral form which this assumes on contraction. 



Mount a specimen in a drop of water together with a bit 



