UNICELLULAR ORGANISMS 



75 



INTERMEDIATE ORGANISMS 



The organisms thus far described are always classed as ani- 

 mals. We will now study two similar organisms, which stand 

 midway between animals and plants. 

 They are closely related, and yet one 

 of them is not infrequently classed as a 

 plant, while the other is almost always 

 placed with the animals. 



PBRANEMA 



Peranema is a microscopic organism 

 found in stagnant fresh water; Fig. 29 A . 

 It is elongated and tapers slightly in 

 front. At the narrower end, which is 

 carried forward in locomotion, there 

 projects a long motile flagellum, by 

 the motion of which the animal is moved 

 through the water. At the base of this 

 flagellum is an opening in the animal, 

 constituting a mouth, leading into a 

 short ossophagal tube. At the bottom 

 of this tube is a peculiar little rod-shaped 

 organ, which apparently serves as a suck- 

 ing organ for seizing food. Near by is 

 a clear contractile vacuole. The proto- 

 plasm of which the body is made is ex- FIG. 29. Two SINGLE- 

 tremely flexible, and the animal, instead CELLED ORGANISMS RE- 

 of retaining its shape, shows a variety 

 of irregular wavelike contractions pass- 

 ing from end to end. A nucleus is 



present, and the animal moves either Bother respects they are much 

 by the motion of its flagella or by 



creeping somewhat after the fashion of the Amoeba. As it 

 possesses a mouth and an cesophagal tube, it lives on solid 



SEMB LING BOTH ANIMALS 

 AND PLANTS 



A, Peranema; B, Euglena. 

 Peranema is a colorless animal, 

 while Euglena is bright green; 



