I PHYLUM PROTOZOA 45 



phorescent, and are usually the agents by means of which 

 the diffuse phosphorescence of the sea is produced. Others, 

 again, are saprophytes, while others are parasites of higher 

 animals. 



3. THE INFUSORIA 



Often to be found in great numbers, in stagnant pools, 

 organic infusions, etc., is Paramecium, the " slipper-shaped 

 animalcule," a Protozoan of comparatively large size, about 

 \ mm. in length, which moves about very actively like 

 Euglena, but with a more regular and more rapid move- 

 ment, and by means of organs of locomotion differing in 

 character from the flagellum of the latter. The body of 

 Paramcecium (Fig. 18, A, B) is covered with what appear 

 under the microscope like small delicate hairs arranged in 

 longitudinal rows. These are the cilia; they are in inces- 

 sant to-and-fro vibration, and it is by their means that the 

 Paramcecium moves about and obtains its food. In shape 

 the body is somewhat cylindrical, rounded at the anterior 

 and bluntly pointed at the posterior end. On one side, 

 the ventral, is a large oblique depression, the buccal groove 

 (buc. gr), leading into a short gullet (gul), which, as in 

 Euglena, ends in the soft internal protoplasm. The proto- 

 plasm is differentiated into a firmer superficial layer, the 

 cortex (cort), and a semi-fluid central mass, the medulla 

 (med), and is covered superficially by a thin cuticle. The 

 cilia are prolongations of the cortex, and perforate the 

 cuticle. 



In the cortex are found two nuclei. One of these, the 

 mcganucleus («//), is a comparatively large ovid body; the 

 other, the micronucleus {pa. mi), is a small rounded body 

 closely applied to the meganucleus. Two contractile 



