PARAMECIUM 151 



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 hairlike projections of the ectosarc 

 through pores in the cuticula. Sensation is exercised by the entire 

 surface of the body. Place a minute crystal of salt on the slide 

 and observe the reaction of the animals to it. 



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 inde- 

 pendent animal and grows to full size. Look among a large num- 

 ber 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 inter- 

 change of micronuclear 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 

 hfe conditions. The change in the structure of the micronucleus 

 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 individuals. 

 Observe them carefully and draw them. 



