AMCEBA. 87 



movements are effected in any direction on a flat surface. 

 Lastly, the treacle processes cannot be again withdrawn 

 unless the inclination of the surface be reversed, whereas 

 the processes of Amoeba may be, and often are, withdrawn. 

 These processes are termed pseudopodia. If the flow of 

 protoplasm be maintained in one particular pseudopodium, 

 it results in a locomotion of the whole animal. 



The body is not the same throughout in appearance and 

 structure. A thin superficial layer of more dense and clear 

 protoplasm, the ectoplasm^ can be distinguished 

 from the more fluid interior formed of endo- 

 plasm. In the endoplasm we can discern numerous 

 bodies. The majority of these are food-particles which lie 

 in small spaces, called food-vacuoles^ but in addition we 

 can usually recognise the nucleus and the contractile vacuole. 

 The nucleus lies loosely in the endoplasm and appears in 

 the living animal like a clear glassy sphere. It consists 

 of nucleoplasm differing somewhat in composition from 

 protoplasm. 



The contractile vacuole is a large spherical space filled 

 with colourless fluid and always lies in or immediately 

 below the ectoplasm. It gradually expands in size and then 

 its walls suddenly contract. A temporary passage or duct 

 is formed through the ectoplasm to the exterior by which 

 the fluid is extruded. The same process is then repeated. 

 This contractile vacuole is usually interpreted as an 

 excretory organ for removing waste nitrogenous matters. 

 Lastly, there are scattered throughout the endoplasm minute 

 granules, the meaning of which is not known, small regular 

 crystals, and particles of debris such as sand grains. 



If Amoeba be subjected to a rise in temperature the 

 movements become more and more active, but when a 

 temperature of about 35 °C. is reached the pseudopodia are 

 withdrawn, the animal assumes a contracted spherical shape, 

 and at about 4o°C. it perishes. Amoeba also reacts to chemical 

 and electrical stimuli, but in every case the whole protoplasm 

 reacts. In other words, there are no definite sense-organs 

 nor nervous system. 



We have already seen the method of locomotion by 

 pseudopodia. When Amoeba in the course of its slow 



