AMCEBA, PARAMCECIUM AND VORTICELLA 41 



body with a smaller oval one attached to its side, the former 

 being the macronucleus, the latter the micronucleus. Note 

 that there are two contractile vacuoles in the Paramcecium; 

 also that the food-vacuoles have a definite course in their 

 movement inside the endosarc. 



Make a drawing of a Paramcecium. 



In comparing Paramcecium with Amceba it is apparent 

 that the body of the first is less simple than that of the second. 

 The definite opening for the ingress of food, the two nuclei, 

 the fixed cilia, and the definite cell-wall giving a fixed shape 

 to the body, are all specializations which make Paramcecium 

 more complex than Amceba. But the whole body is still 

 composed of a single cell, and there is, as in Amceba, no 

 differentiation of the body-substance into different tis- 

 sues, and no arrangement of body-parts as systems of 



organs. 



Paramcecium may occasionally be found reproducing. 

 This process takes place very much as in Amceba. The 

 animal remains dormant for a while, the micronucleus then 

 divides, the macronucleus elongates and finally divides in 

 two, the protoplasm of the body becomes constricted into 

 two parts, each part massing itelf about the withdrawn 

 halves of the macro- and micronuclei, and lastly the whole 

 breaks into two smaller organisms which grow to be like the 

 original. After multiplication or reproduction has gone on 

 in this way for numerous generations (from one to two 

 hundred), a fusion of two Paramcecia seems necessary before 

 further divisions take place. (This is probably true of Am- 

 ceba also.) This process of fusion, called conjugation, may 

 be noted at some seasons. Two Paramcecia unite with 

 their buccal grooves together, part of the macronucleus 

 and micronucleus of each passes over to the other, and the 

 mixed elements fuse together to form a new macro- and 

 micronucleus in each half. The conjugating Paramcecia 

 now separate, and each divides to form two new individuals. 



