CHAPTER XXXII. ETJGLENA. 



1. Occurrence and Mode of Life. The organisms dis- 

 tinguished by the name Euglena are minute, unicellular 

 forms of green colour, which occur commonly and often in 

 great abundance in stagnant water containing much organic 

 nitrogenous matter. Pools or ditches which are contami- 

 nated with the urine and excrement of farm animals 

 almost invariably contain Euglenoids of one or more 

 species, and one of the commonest forms is that known as 

 Euglena viridis. The longest diameter of the organisms 

 varies in different species from '03 to '2 mm., so that 

 details of their structure are only to be made out by care- 

 ful examination under high powers of the microscope. 

 The most characteristic condition is that of active motion. 

 So small that they cannot be separately distinguished by 

 the naked eye, but merely give the water containing them 

 a green colour, under the microscope they are seen as green 

 specks moving rapidly in all directions. 



The individual Euglena (fig. 203, A) is a single cell having 

 a spindle-like shape, the end which is foremost as the 

 organism moves being blunt and the opposite end tapering 

 to a point. The body is surrounded by a distinct cuticle, 

 which though firm and strong is very thin and is suffici- 

 ently flexible and elastic to permit of considerable and 

 characteristic changes of form which the body occasionally 

 exhibits. These changes consist of the contraction of one 

 part of the body and the dilatation of another, and are 

 spoken of as Euglenoid when they occur in other Pro- 

 tozoa. The surface of the cuticle is marked by spiral 

 lines or striations, which appear to be delicate ridges on 



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