48 



and in mode of division, the division of the meganucleus 

 being amitotic, and of the micronucleus, mitotic). 



In some instances (e.g., Opalina) there are many nuclei. 

 There is usually a definite mouth which may be at the sur- 

 face or insunk at the bottom of a funnel, the vestibule. 

 There may be one contractile vacuole or many. The modes 

 of reproduction are transverse and longitudinal fission, 

 gemmation or budding, and spore formation. Some Ciliates 

 form colonies (e.g., Epistylis, Carchesium). There are 

 freshwater and marine forms, free-swimming or fixed 

 (often with a stalk), and others are entozoic, i.e., living 

 inside other animals, e.g., Opalina, Balantidium. 



PARAMECIUM. 

 (A type of Infusoria and an example of the Class Ciliata.) 



Describe the General Appearance and Structure of Para- 

 mecium. 



The Slipper Animalcule is visible to the naked eye. 

 It has a definite long oval shape. It is rounded at one 

 (anterior) end and is sharper at the other (posterior) end. 

 The body is covered uniformly with short and delicate 

 cilia (holotrichous). The greater bulk of the body is the 

 endoplasm or medulla, which is full of granules, food vacu- 

 oles, and foreign bodies (e.g., symbiotic algse). Around 

 the endoplasm is the thin ectoplasm or cortex which lias 

 an outer pellicle or cuticle, and in which are the contractile 

 mysneme threads and the trichocysts. On one side about 

 the middle is the opening of the funnel (vestibule or peri- 

 stome) which is richly ciliated. At the bottom of this 

 funnel is the true mouth or cytostome, opening into a short 

 gullet which has a delicate undulating membrane. Two 

 contractile vacuoles are seen at intervals. At first there 

 appears a ring of tiny tributary vacuoles, and these form 

 the large spherical vacuole. It expands (diastole) until 

 it comes in contact with the surface of the pellicle ; then 

 it suddenly contracts (systole) and vanishes. Staining with 



