t. 



PARAMECIUM 187 



Paramecium has no special vegetative organs except the 

 pulsating vacuoles. Food vacuoles are taken into the entosarc 

 through the mouth. Here they circulate for some time, while 

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

 cles that it contains are digested. The indigestible matters are 

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



m 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. 



A process which is universal among infusorians is conjugation. 

 Two individuals place the ventral surfaces of their anterior 

 ends together. In this position their bodies fuse together and 

 an interchange of micronu clear matter takes place between them. 

 The two individuals then separate. 



Conjugation was formerly supposed to be a process by which 

 weak and infertile animals renewed their strength and vitality. 

 It is now supposed to be rather a preparation for unfavorable 

 life conditions. The change in the structure of the micronu cleus 

 leads to a change in the essential characters of the animals, and 

 thus gives them additional powers of environmental adaptation 

 and a better chance to survive unfavorable conditions. 



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

 viduals. Observe them carefully and draw them. 



