124 



General Biology 



although apparently it holds the stage as well as any, and better than 

 most theories at this particular moment. The current seems to start at 

 the foremost part of the animal and extends backward. Jennings has 

 shown that Amoeba verrucosa resembles an elastic sac rilled with fluid. 

 By placing this animal in a substance such as soot, which he caused to 

 surround one of them, it was 



j 



m 



a 



m 



i ' '■ 





c m 



'*. * * - 



shown that the streaming fol- 

 lowed the ectosarc toward the 

 forepart of the animal, and just 

 as it got beneath the Amoeba, 

 remained there until the ani- 

 mal had moved over it, when 

 it again moved upward at the 

 posterior end. 



Dellinger has shown that 



whether on floor or ceiling, 



wherever Amoebae are found 



to move, there is a sort of 



creeping walk by which one or 



more outer parts of the animal 



are extended at random. When 



this projecting part comes in 



contact with a solid substance 



the most posterior attachment 



relinquishes its pseudopod. It 



is, therefore, assumed that 



there is a contractile substance 



within the animal. 



All the various experiments along this line have depended upon 



surface tension for their explanation. However, even if the animal 



moves in a similar manner to a drop of liquid that is not living, it does 



not follow that the same force in each case causes the movement. 



It is essential that all of the subject headings under which the frog 

 was studied should also be borne in mind when the single-celled animals 

 come in for investigation. For example, in regard to metabolism, the 

 following subjects must be studied just as in a more complex organism: 

 Ingestion, digestion, egestion, absorption, circulation, assimilation, dis- 

 similation, secretion, excretion, and respiration. 



It can readily be understood that there must be some instinctive 

 process by which Amoebae know what food to ingest and what not to, 

 or they might continue to take in sand particles and indigestible sub- 

 stances which would cause the body to become so extended and heavy 

 that the animal would die from this effect alone. There are, of course, 

 no organs such as a mouth and intestinal tract, as in the frog. The 

 food is taken in at any point of the body. This food consists of tiny 



Fig. 45. — Locomotion of Amoeba proteus. 



Photographs in side view. A and B show a speci- 

 men attached at two points, a and b, and a pseudopod 

 which projects from one end and bends down to the 

 substratum as in B at d ; C shows the extension of a 

 long pseudopod. (From Hegner after Dellinger.) 



