56 



COLLEGE ZOOLOGY 



may be designated oral, and the opposite 

 side, aboral. The motile organelles are fine 

 hairlike cilia regularly arranged over the 

 surface. As in the amoeba, two types of 

 cytoplasm are visible: an outer compara- 

 tively thin clear layer, the ectoplasm; and 

 an inner granular mass, the endoplasm. Be- 

 sides these, a distinct elastic membrane, the 

 pellicle, is present on the outer surface of 

 the ectoplasm. One large contractile vacu- 

 ole is usually situated near each end of the 

 body, close to the aboral surface; and a 



variable number of food vacuoles may be 

 seen. The nuclei are two in number, a large 

 macronucleus concerned with vegetative 

 functions, and a smaller micronucleus that 

 is important in reproduction; these are sus- 

 pended in the endoplasm near the mouth 

 opening. A temporary opening called the 

 cell anus can be observed only when undi- 

 gested particles are discharged. It is situated 

 posterior to the oral groove, and it always 

 reforms at the same point on the surface of 

 the body. 



Cilium 



Pellicle 



Trichocyst 

 opening 



Basal body 

 of cilium 



TrichocysJ 



fnferciliary 

 fibril 



Figure 26. PuTameciurn. Diagram showing structure of the pellicle: the hexagonal areas are due 

 to ridges; the cilia extend out from the center of the hexagonal areas, each being attached to 

 a basal body; the basal bodies are located on longitudinal fibers; these fibers appear to constitute 

 the mechanism by which the activity of the cilia is coordinated. The carrot-shaped trichocysts 

 are attached by delicate threads to the ridges. Highly magnified. (After Lund.) 



The endoplasm occupies the central part 

 of the body. Most of the larger granules con- 

 tained within it are shown by microchemical 

 reactions to be reserve food particles; they 

 flow from place to place, indicating that the 

 endoplasm is of a fluid nature. The ecto- 

 plasm does not contain any of the large gran- 



ules characteristic of the endoplasm, since 

 its density prevents their entrance. In this 

 respect the two kinds of cytoplasm resemble 

 the ectoplasm and endoplasm of the amoeba. 

 If a drop or two of 35 per cent alcohol ia 

 added to a drop of water containing para- 

 mecia, the pellicle will be raised in some 



