ix.l THE BELL-ANIMALCULE. 93 



state of existence. In thus passing into a temporary condi- 

 tion of rest many of the other Infusoria resemble Vorticella. 



The two genera of Infusoria which most commonly occur 

 in the Frog are Nyctotherus and Balantidium. Both are 

 free and actively locomotive, and the former is particularly 

 remarkable for its relatively large size and semilunar con- 

 tour, and for the length and distinctness of its curved oeso- 

 phagus. Balantidium is pyriform, and has a very short 

 cesophageal depression. 



LABORATORY WORK. 



Examine duckweed roots, confervae, &c., with \ inch 

 objective avoiding pressure ; having found a group of 

 Vorticellcz note the following points with a higher 

 power. 



In the extended state of the animal, 

 a. The body. 



a. Its size (measure). 



b. Form; broadly speaking, that of an inverted 

 bell : note 



a. The prominent everted rim (peristome). 



p. The flattened central disc projecting -above 



the peristome. 



y. The cilia fringing the disc, 

 o. The depression between the peristome and 



disc. 

 c. The mouth of the chamber (vestibuluni) into . 



which the oesophagus and anus open, in the 



hollow between the peristome and disc. 



