THE SLIPPER ANIMALCULE 



(iv) The spongy layer, the innermost portion of the ectoplasm, in 

 which fluid from the endoplasm collects. This fluid gathers 

 particularly in two sets of radiating channels or collecting 

 canals, and these drain off to form two large central drops, 

 the contractile vacuoles. The formation or expansion {dia- 

 stole) of each vacuole goes on until it comes into contact 

 with the pellicle, then sudden contraction {systole) occurs, 

 and the large spherical vacuole disappears. This process is 

 repeated at brief intervals. The two vacuoles always re-form 

 about the same position, between the centre and each end of 

 the body. 

 The other structures connected with the ectoplasm are : 



(v) The cilia, numerous delicate vibratile filaments arranged in 

 longitudinal rows over the whole outer surface. In the 

 gullet specially large cilia adhere together and there form an 

 undulating membrane, 

 (vi) The oral groove or peristome, which begins near the anterior 

 end of the Paramecium and leads to the mouth, which opens 

 into the gullet. The food particles, carried in by the action of 

 the peristome cilia, pass through the mouth into the gullet, 

 and are there driven onward by the undulating membrane. 

 The food vacuoles are formed at the bottom of the gullet and 

 carried into the endoplasm. To see the formation of food 

 vacuoles, put a drop of Indian ink at the edge of the cover- 

 slip and watch the ingestion of the ink particles, 

 (vii) The potential anus, a spot in the cortex, situated about midway 

 between the mouth and the posterior end of the animal, and 

 only visible when the waste products are extruded. 



(6) The endoplasm, endosarc or medulla, which is granular and fluid, and 

 which forms the central portion of the body. In the endosarc the 

 following structures may be seen : — 



(i) The food vacuoles, spaces containing the particles of food, 

 (ii) The macronucleus or meganucleus, a large ovoid body situated 

 near the middle of the cell. This nucleus is concerned with the 

 ordinary life of the body, 

 (iii) The micronucleus, a very much smaller body lying at the 

 side of the macronucleus. It is specialised for reproduction. 

 Some species, e.g., Paramecium aurelia, have two micronuclei. 

 Make a sketch of Paramecium, to show the above features. 



