294 Descriptive Zoology. 



be seen to contract at tolerably frequent intervals, appar- 

 ently discharging liquid to the exterior. Around each of 

 these " contractile vacuoles " is a series of radiating canals. 

 After the vacuole has become obliterated by emptying its 

 contents, it is gradually filled again by these surrounding 

 canals, which get watery material from the various parts 

 of the body. Thus certain waste material is thrown out. 



The Nucleus. Paramecium has two nuclei, a larger 

 body called the macronucleus and a smaller called the 

 micronucleus. 



How Paramecium protects Itself. In the outer part, 

 or cortex, are many small sacs, each containing a tiny 

 thread. When a paramecium is irritated, it discharges 

 these thread-cells, which appear to produce a stinging or 

 benumbing effect on small animals. 



Multiplication of Paramecia. Like the amoeba and 

 the vorticella, the paramecium forms new individuals by 

 division. The constriction is transverse, at about the 

 middle, and finally separates the one into two. Both the 

 macronucleus and the micronucleus divide, a part going 

 with each half, which soon after separating becomes a 

 complete paramecium. 



VorticeJa, the Bell Animalcule. Another interesting 

 protozoan is Vorticella or the bell animalcule. It is 

 found on submerged stems and leaves in stagnant water, 

 sometimes appearing like a delicate white fringe. Under 

 a low power of the microscope a vorticella is seen to be 

 bell-shaped, attached by a slender, flexible stalk, which 

 joins the handle end of the bell-shaped body to some solid 

 object. When the animalcule is disturbed, the stalk be- 

 comes coiled, jerking the body up close to its support, 

 where it is much more secure than when extended. 



