7";^!? Ufticelbilar Organisms. 3 



shape, which has no fixed position, but moves about with the 

 movements of the animal ; this is termed the nucleus. In 

 many amoebae a clear vesicle also exists (the contractile vacuole), 

 which, if kept under the eye for a few minutes, will be noticed 

 to suddenly contract — apparently expelling its fluid contents — 

 and to gradually fill out again, repeating the process continually. 



This is positively the entire anatomy of the amoeba, stated, 

 of course, very briefly. No animal simpler in structure than 

 this organism is certainly known. Some amoebae lack the 

 contractile vacuole ; but all consist of a mass of the jelly-like 

 living matter (^protoplasm) and a nucleus or nuclei. It has 

 been stated that there are amoeboid creatures without a 

 nucleus ; but this does not appear to be by any means certain. 

 And we shall see later that it is improbable. 



The amoeba not only has the certain definite structure that 

 has just been briefly described ; it also acts ; the living matter 

 of which it is built up performs certain functions. We have to 

 consider the physiology (the functions) of the amoeba, as 

 well as its structure (its morphology). The movements of the 

 animal have been already referred to. It is continually in 

 motion, and the movements may be retarded by cold, increased 

 by warmth, and again retarded and stopped by too great 

 warmth. Various chemical substances produce similar effects. 

 The living matter, therefore, of which the amoeba is composed 

 is capable of movement, and is irritable — that is, responds to 

 stimuli. If an amoeba be watched for some time it will be 

 seen to feed. It takes in nourishment by simply flowing over 

 and engulphing a minute plant or other organism ; it literally 

 gets outside its food. After a time the ingested food particle 

 will be seen to gradually disappear, and the indigestible residue 

 may be seen to be thrust out of the body. Furthermore, the 

 contractions of the contractile vacuole expel from the body 

 other waste substances. If an amoeba be kept in filtered 

 water, in which there is no vegetable or animal matter, it will 

 die after a longer or shorter time. Nor will it avail it that the 

 water be impregnated with the various chemical elements, or 

 compounds of them, that make up its body. The amoeba 

 needs organized matter to feed upon. 



