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General Biology 



(4) Phototropism, meaning a reaction to light; 



(5) Electrotropism, meaning a reaction to an electric current; 



(6) Geotropism, a reaction to gravity; 



(7) Chromotropism, a reaction to color; 



(8) Rheotropism, a reaction to current. 



Amoebae move away from strong light, so that they are said to be 

 negatively phototropic. They are also negatively thigmotropic. 



If an action is self-imposed, it is said to be autogenous 

 ( ) ; if an external object causes a reaction, whether 



such object be located within or without the body, the action is known 

 as etiogenous ( ). 



EUGLENA 



This little organism (Fig. 48) moves about like a full-fledged ani- 

 mal although it has chlorophyl in its body and manufactures its food 



as does the plant; and it does this notwith- 

 standing the fact that it has a mouth and 

 gullet. 



Euglena belongs to the Class Mas- 

 tigophora ( ), which 



means that there is a whip-like flagellum 

 protruding from its anterior end. Several 

 animals must be grouped together in order 

 that the naked eye may see any organisms 

 present. When there are many in one place 

 a characteristic green color is given the sur- 

 rounding water. 



EXTERNAL AND INTERNAL 

 FEATURES 



Euglena viridis is a single celled, 

 elongated animal pointed at the posterior, 

 and blunt at the anterior end. As in 

 Amoeba, there are two layers in the cyto- 

 plasm, the ectosarc, a dense outer layer, and 

 the endosarc, a more fluid central mass. 

 There is a thin cuticle running in parallel 

 thickenings around the body of the animal 

 in an oblique direction so that it appears 

 striated. 



The mouth is a funnel-shaped depression lying a little to one side 

 of the center of the anterior blunt end. The gullet is a continuation of 

 this depression. It looks like a duct, and connects with a large spherical 



A. Euglena viridis; m, the so- 

 called mouth; n, the nucleus; e, 

 the stigma; r, reservoir; c.v., con- 

 tractile vacuoles; _ chr, _ chromato- 

 phors; am, pyrenoids with sheaths 

 of paramylum. B, another speci- 

 men, showing change of shape and 

 diagonal striation of the cuticle. C 

 and D, outlines to show various 

 stages of contraction. E, a free 

 swimming specimen undergoing 

 longitudinal division. F and G, divi- 

 sion of an encysted form. (A-D, 

 after Bourne; E-G, after Stein.) 



