CHAPTER XVI 



PARAMECIUM 



A MORE COMPLEX PROTOZOAN 



The Paramecium may serve as an example of a one-celled animal in 

 which there is a considerable degree of specialization. Certain parts 

 of the body are permanently modified for the performance of particular 

 functions, a process generally known as division of labor. 



98. Occurrence. — Paramecia appear in abundance in any water in 

 which there is a considerable amount of decaying organic matter. They 

 abound in streams and all bodies of water polluted by the entrance of 

 sewage, feeding upon the bacteria which swarm in such water, and 

 frequently appear in ameba cultures in which there is an accumulation 

 of decaying animal and plant matter. 



Since paramecia tend to gather at the surface and especially in contact 

 with floating objects, they frequently form a white scum. They may, 

 however, be found throughout the bodies of water in which they live. 



99. Structure. — Paramecia (Fig. 19) are elongated in form and are 

 frequently described as cigar-shaped, the anterior end being blunt and the 

 posterior more pointed. Because the form is similar to that of a slipper, 

 the anterior end representing the heel and the posterior the toe, they have 

 been called slipper animalcules. A groove called the oral groove, or 

 'peristome, starts at the anterior end of the animal and runs obliquely 

 backward from right to left or left to right, ending a little behind 

 the middle of the body. If one were to conceive of himself looking at the 

 Paramecium from in front, this could be expressed by saying that the 

 groove may run in a clockwise direction, which would be the direction 

 corresponding to the direction of motion of the hands of a clock, or in a 

 counterclockwise direction, which would be the opposite. In Paramecium 

 caudatum Ehrenberg the groove usually runs clockwise, but in cultures in 

 which this is the prevailing type others may be found. Occasionally 

 a culture will appear in which the majority of the individuals show a coun- 

 terclockwise direction. The body is covered with fine hairlike cilia, 

 which in the species referred to are longer at the posterior end. Near 

 the end of the oral groove is an opening known as the mouth. This 

 leads into a gullet, which is a cleft running a short distance back into the 

 cytoplasm. 



Over the whole surface of the body is a colorless, elastic membrane 

 known as the pellicle, or cuticle. This seems to be divided by raised lines 



69 



