PARAMCECIUM. 



95 



soak for some days in a glass of water. A few individuals have 

 been lying dormant about the plant ; they revive and multiply 

 with extraordinary rapidity. They are also abundant in most 

 stagnant pools, and are just visible when a test-tube contain- 

 ing them is held between the eye and the light. Their food 

 consists of small vegetable particles. 



The form is a long oval, with the blunter end in front ; 



FIG. 40. Conjugation of Paramoscium aurelia four 

 stages. After Maupas. 



1. Shows macronucleus (N) and two micronuclei () in each ot 



the two conjugates. 



2. Shows breaking up of macronucleus, and multiplication of 



micronuclei to eight. 

 3- Shows the fertilisation in progress ; the macronucleus is 



vanishing. 

 4. Shows a single (fertilised) micronucleus in each conjugate. 



the outer portion of the cell substance is differentiated into 

 a dense rind or cortex, with a delicate external cuticle, 

 perforated by cilia. There is a definite opening, the so- 

 called mouth, which serves for the ingestion of food 

 particles , and there is also a particular anal spot posterior 



FIG. 41. Diagrammatic expression of process 

 of conjugation in Paramcecium aurelia. 

 After Maupas. 



A. The two micronuclei enlarge. 



B. Each divides into two. 



C. Eight micronuclei are formed. 



D. Seven disappear ; one (darkened) divides into two. 



E. An interchange and fusion occurs, and the con- 



jugates separate. 



F. The fertilised micronucleus divides into two. 



G. Each conjugate begins to divide, the micronucleus 



of each half dividing into two, one of which 

 becomes the macronucleus, while the others form 

 the two normal micronuclei. The top line repre- 

 sents four individuals, each with a macronucleus 

 and two micronuclei. 



to the mouth, from which undigested residues are got rid of. 

 The surface is covered with cilia, in regular longitudinal 

 rows ; these serve both for locomotion and for driving 



