PARAM^CIUM CAUDATUM EHRENBERG 5 



latter ends in the endoplasm. A food vacuole is formed around 

 the food thus drawn in. It detaches itself from the end of the 

 cytopharynx and moves through the endoplasma first down- 

 ward, then upward and again downward. During this cyclosis 

 or travelling through the endoplasma the food particle is digested 

 and at the end of the process the waste matter is emptied through 

 the cytopyge. 



Reproduction. Asexual reproduction is the usual method 

 and consists in a transverse division. This is initiated by changes 

 in the micronucleus which is essentially a reproductive organ- 

 ellum. It becomes elongated and its chromatic substance shows 

 an arrangement similar to that in mitosis of cells in higher 

 animals, yet without the presence of a centrosome. The cyto- 

 stome, too, becomes elongated and compressed in the middle to 

 the shape of a narrow slit. The cytopharynx produces pos- 

 teriorly a new cytopharynx. Two new pulsating vacuols are 

 formed so that each daughter individual will receive an old and 

 a new vacuole. Next the macronucleus becomes also elongated. 

 A constriction appears in the middle of the animal which at 

 this stage of its life is almost twice as long as usual. Finally both 

 nuclei divide in two, their division is followed by a division of the 

 protoplasm and the two halves of the original Paramaecium be- 

 come independent individuals. Each is provided with all nec- 

 essary organella, assumes the shape of a normal Paramaecium 

 and is soon ready to divide again. Such transverse division may 

 go on for from 80 to 100 generations, but sooner or later a re- 

 organization of the nuclear apparatus has to take place in order 

 that the race should not die out. This is accomplished by a 

 process recently discovered by Woodruff. The micronucleus 

 divides twice. Three of the four micronuclei thus formed dis- 

 integrate and are resorbed by the protoplasm. The fourth 

 micronucleus alone persists. The macronucleus which is es- 

 sentially a vegetative nucleus, breaks up and is also resorbed 

 by the protoplasm. A new macronucleus is formed from the 

 micronucleus in a way similar to that in conjugation. 



