128 AN INTRODUCTION TO ZOOLOGY 



with a slow circulatory movement termed cyclosis, which can readily 

 be seen in the living animal. The granules in it are of several sorts. 

 The reserve food material takes the form of small particles of animal 

 starch or glycogen, and can readily be stained with Iodine which 

 turns them a wine red. Some of the granules of excretory matter 

 appear to take the form of Calcium phosphate. The remaining 

 granules are mostly the indigestible remains of the food. Food 

 vacuoles similar to those in Amoeba containing a certain amount of 

 fluid and food in a more or less digested state are also present, and 

 render the cyclosis very distinct. 



Near the middle of the cell, not far from the cytopharynx, is a 

 fairly large ovoidal body that stains uniformly and very intensely 

 with basic stains. This is the meganucleus or macronucleus, and 

 near it closer examination will reveal the presence of a much smaller 

 and more lightly staining granule, the micronucleus. Thus, unlike 

 Amoeba, the nuclear matter in Paramcecium is contained in two 

 separate nuclei, each with its own particular function. 



It has already been noted that Paramcecium is a free- 

 swimming animal moving relatively quickly by means of its cilia. 

 As it moves forward it not only rotates on its own axis, but the path 

 it traces is similar to a spiral line drawn on a cylinder. On striking 

 a solid object it is able suddenly to reverse the action of its cilia 

 for a very brief period, and so it recoils a short distance. When it 

 is necessary to change the direction of its course it appears to be able 

 to keep the posterior end relatively still while the anterior end rotates 

 in a small circle. It then moves off at an angle to its former course, 

 and several such movements are required to reverse completely the 

 direction of its progress. As in A mceba, its movements maybe divided 

 into spontaneous and induced, and, indeed, it shows very marked 

 reactions to mechanical, chemical, thermal and electrical stimuli. 



The cilia covering the anterior end are arranged in curved rows 

 pointing into the peristome groove, so that food particles, consisting 

 mainly of bacteria, are gradually driven towards the cytostome. 

 In the cytopharynx the cilia are arranged in a special way. There 

 is a row of long modified cilia partially fused so as to form a ribbon- 

 like structure known as the undulating membrane. This, by its 

 wave-like movements, takes the food particles down to the endoplasm 

 where they accumulate in small masses which, when they reach a 

 certain size, become surrounded by a vacuole and pass into the 

 general circulation brought about by the cyclosis of the endoplasm. 

 Within the food vacuole digestion takes place in a manner doubtless 

 similar to that in Amoeba. A very instructive idea of the part 

 played by the macronucleus in the activities of the cell can be 

 gathered by over-feeding the animal. Under this treatment its 



