THE PROTOZOA 



125 



T/flCHOCYQTS 



the vital phenomena characteristic of all plants and animals, namely, 

 contractility, irritability, metabolism, growth and reproduction. 



Free- Living Protozoa ii. Paramcecium. 



The genus Paramcecium, like the genus Amceba, contains a number 

 of separate species of which P. aurelia and P. caudatum are the 

 commonest, but these only 

 differ from one another in 

 comparatively small points, 

 and a general description will 

 serve equally well for either 

 species. From its somewhat 

 fanciful resemblance to a slip- 

 per, the animal receives its 

 popular name of the slipper ******* 

 animalcule. It is to be found 

 plentifully in ponds and 

 ditches, and belongs to that 

 class of the Protozoa known 

 as the Infusoria, from the fact 

 that they appear in infusions 

 of organic matter that are ex- 

 posed to the air.* 



Paramcecium differs con- 

 siderably from Amceba in 

 several important respects : it 

 is larger, reaching a length of 

 0-3 mm., and so is just visible 

 to the naked eye as a tiny 

 whitish speck ; it has a definite 

 shape ; it is not a creeping 

 form, but swims about actively, 

 and altogether it is a higher 

 form, having reached a con- 

 siderable degree of structural 

 complexity. In shape it is 

 somewhat like a cigar, one FIG. 

 end is bluntly rounded, and as 

 it lies foremost in locomotion 

 is the anterior end. The opposite or posterior end is more pointed 



* A very simple infusion can be made by putting chopped hay into water, 

 bringing it to the boil and then allowing it to cool. If this be placed aside in a 

 cool spot in the open air Paramcecium of several species will appear in it 

 after a few days, and subsequently an enormous number will be found. 



CONTRACTILE 



39. Diagram of structures of 

 Paramcecium caudatum. 



