PARAMCECIUm. 



91 



soak for a few days in a glass of water. A few Infusorians 

 have been lying dormant about the plant ; they revive and 

 multiply with extraordinary rapidity. They are abundant in 

 most stagnant pools, and are just visible when a test tube 

 containing them is held between the eye and the hght. 

 Their food consists of small vegetable particles. 



The form is a long oval, the outer portion of the cell 

 substance is differentiated to form a definite rind. With 

 this we may associate the fact that there is now a definite 

 opening, the so-called mouth, which serves for the ingestion 



COD 



Fu;. 20. — Paraino:ciHiii. (After BuTSCIILl). 



ad. Adult form, showing cilia, " mouth," contr^ictile \-acuoles, eLc. 

 div. Transverse division. 

 C071. Conjugation. 



of food particles. The surface is uniformly covered with 

 cilia, arranged in regular longitudinal rows ; these serve 

 both for locomotion and for driving food particles towards 

 the mouth. Among the cilia on the cortex there are small 

 cavities, in which lie fine protrusible threads ("trichocysts"). 

 These, though parts of a cell, suggest the thread cells of 

 Ccelentera, and are probably of the nature of weapons. 

 In the substance of the cell lie two nuclei, the smaller 



