GJENERAL BIOLOGY. 13 



nNICIIIiZ.UIjAR ANIMALS. 



The Peoteus Animaioot-e {Amo&ba). 



In order to illustrate animal life in its simpler form we 

 choose the above-named creature, which is nearly as readily 

 obtainable as Protococcus and often under the same circum- 

 stances. 



Morphological. — Amoeiba is a microscopic mass of transpar- 

 ent protoplasm, about the size of the largest of the colorless 

 blood-corpuscles of cold-blooded animals, with a clearer, more 

 consistent outer zone (ectosarc), (although without any proper 

 cell wall), and a more fluid, granular inner part. A clear space 

 (contractile vesicle, vacuole) makes its appearance at intervals 

 in the ectosarc, which may disappear somewhat suddenly. This 

 appearance and vanishing have suggested the term pulsating 

 or contracting vesicle. Both a nucleus and nucleolus may be 

 seen in Amoeba. At varying short periods certain parts of its 

 body (paeudopodia) are thrust out and others withdrawn. 



Physiological. — Amoeba can not live on such food as proves 

 adequate for either Protococcus or Torula, but requires, besides 

 inorganic and unorganized food, also organized matter in the 

 form of a complex organic compound known as protein, which 

 contains nitrogen in addition to carbon, hydrogen, and oxygen. 

 In fact. Amoeba can prey upon both plants and animals, and 

 thus use up as food protoplasm itself. The pseudopodia serve 

 the double purpose of organs of locomotion and prehension. 



This creature absorbs oxygen and evolves carbon dioxide. 

 Inasmuch as any part of the body may serve for the admission, 

 and possibly the digestion, of food and the ejection of the use- 

 less remains, we are not able to define the functions of special 

 parts. Amoeba exercises, however, some degree of choice as to 

 what it accepts or rejects. 



The movements of the pseudopodia cease when the tempera- 

 ture of the surrounding medium is raised or lowered beyond a 

 certain point. It can, however, survive in a quiescent form 

 greater depression than elevation of the temperature. Thus, at 

 35° C, heat-rigor is induced; at 40° to 45° C, death results ; 

 but though all movement is arrested at the freezing-point of 

 water, recovery ensues if the temperature be gradually raised. 

 Its form is modified by electric shocks and chemical agents, 

 as well as by variations in the temperature. At the pres- 

 ent time it is not possible to define accurately the functions 



