168 life's beginning on the eaeth 



C. The Shape of Pseudopodia 



There are many different species of Amoeba. One of 

 their marks of distinction is the form of their pseudopodia. 

 Some animals have extremely slender ones, so that they 

 resemble delicate hairs, of which a large number surrounds 

 the Amoeba everywhere; other animals have broad pseu- 

 dopodia which, when protruding, seem to distort the entire 

 animal. 



Experiments with oil-drops show that their protrusions 

 can likewise be produced in any form, by using various kinds 

 of oil and different additions to the surrounding water. 

 Figure 66 shows how the oil drop can be distorted, or caused 

 to send out protrusions in the most diversified manner. 



In the oil-drop the varying shape is the result of the 

 chemical composition of the oil, or of the surrounding watery 

 solution. It is very likely that a similar factor accounts for 

 the shapes of the various species of Amoeba. 



I). The Selectiori of Food 



In the selection of its food, the Amoeba also shows a most 

 striking resemblance to an oil-drop, incredible as this may 

 seem. H. S. Jennings, Professor of Zoology at Johns Hop- 

 kins University describes this resemblance very clearly: 



One of the most striking phenomena in the behaviour of Amoeba is its 

 power of selecting substances which shall serve as food. Amoeba takes its 

 food simply by sending out pseudopodia, flowing around and enveloping 

 small bodies. But it by no means takes these at random; sand, decayed 

 plant tissue, bits of wood, dirt, etc., are as a rule rejected, while small 

 living plant and animal cells, diatoms, infusoria, are enveloped, carried 

 away and digested. It thus shows a distinct choice in the substances 

 which it takes into itself, and the power of choice has often been considered 

 evidence of a rather highly developed mind. 



Before accepting this conclusion for Amoeba, it will be wise to test this 

 matter of the power of choice for other fluids. A drop of chloroform is a 

 good subject for experimentation. With a medicine dropper a drop of 



chloroform may be placed in the bottom of a watch-glass of water, and t hen 

 with fine tweezers we may offer it various substances to test its power of 



