I'AllAMECIUM 167 



Paramecium has no special vegetative organs except the 

 pulsating vacuoles. Food vacuoles are taken into the endosarc 

 through the mouth. Here they circulate for some time while 

 the water forming the vacuole is absorbed and the food par- 

 ticles it contains are digested. The indigestible matters are 

 collected at a spot just back of the mouth and are there ejected 

 from the body through a temporary opening in the ectosarc, 

 which forms for that purpose ; the water of the food vacuole 

 is collected in the pulsating vacuoles and ejected. Respiration 

 is carried on through the external surface of the body. The 

 organs of locomotion are the cilia, which are distributed evenly 

 over the surface of the body ; they are hair-like projections of 

 the ectosarc through pores in the cuticula. Sensation is exercised 

 by the entire surface of the body. 



Reproduction is asexual, by division. A transverse constric- 

 tion appears in the surface of the middle of the animal's body 

 and deepens until it is divided in two. Each half becomes an 

 independent animal and grows to full size. Look among a 

 large number of animals for one which is dividing. 



The process of reproduction is closely connected with that of 

 nutrition. Animals which are not surrounded by the proper 

 conditions of nutrition gradually lose their vitality and repro- 

 ductive powers. The offspring gradually become smaller and 

 divide less frequently, and from time to time find it neces- 

 sary to go through a peculiar rejuvenating process which is 

 called conjugation. Two individuals place the ventral surfaces 

 of their anterior ends together. In this position their bodies 

 fuse together and an interchange of nuclear matter takes place 

 between them. The two individuals then separate ; the process 

 has renewed their vitality, and they again reproduce rapidly. 



Exercise 4. Look for dividing and also for conjugating indi- 

 viduals. Observe them carefully. Draw outlines of those 

 observed. 



