CHAPTER IX 



THE FLAGELLATA EUGLENA VIRIDIS, COP- 

 ROMONAS SUBTILIS, AND POLYTOMA UVELLA 



IT was known to the earliest microscopists that water contain- 

 ing organic matter in solution soon becomes tenanted with 

 swarms of microscopic animalcules, and that of these different 

 kinds succeed one another in a more or less regular order. 

 The first stage is that of putrescence, a phenomenon due to 

 the development of a vast number of Bacteria, which after a 

 time become quiescent, form spores, and seem to disappear. 

 They are succeeded by swarms of other animalcules of larger 

 size, usually characterised by the possession of one or more 

 relatively long, transparent and very fine processes of proto- 

 plasm, which by their lashing movements propel the organisms 

 through the water. These protoplasmic processes have been 

 aptly likened to whip-lashes, and hence the organisms possess- 

 ing them have been called the Mastigophora, or whip-bearers, 

 whilst a subdivision of the group is known by the name of the 

 Flagellata. One of the commonest as also one of the largest 

 of these forms is an animalcule of a deep green colour, which 

 is frequently found in such abundance in puddles of rain-water 

 impregnated with decaying vegetable matter that the water 

 appears of a uniform dark green tint, easily distinguished from 

 the green colour imparted to ponds by the presence of fila- 

 mentous algae, since the latter are visible to the naked eye 

 when a glass vessel containing them is held up to the light. 

 Our animalcule, indistinguishable by the naked eye, is known 

 as Euglena. There are many species of Euglena, differing in 

 the shape and proportions of their bodies, but agreeing in all 

 essential particulars with the species called Euglena viridis, 

 which we will take as a type. An individual of this species 

 has the form depicted in fig. 40. Its body consists of a single 

 elongated cell, tapering to a point at one extremity. The 

 opposite extremity is blunt and obliquely truncated, and, as it 

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