THE PROTOZOA-THE DAWN OF LIFE 19 



these organisms, so that the old, and at times bitter, controversy 

 as to whether such and such an order of the Flagellata should 

 be placed among the unicellular plants, or among the Protozoa, is 

 practically ended, Professor Haeckel's term Protista sufficiently 

 describing their somewhat elusive character. 



Living urder varying conditions, the Flagellata exhibit vari- 

 ous methods of nutrition. Some of the simplest forms live in 

 liquids containing decaying organic matter, which they absorb 

 through their surface ; 1 some engulf their food either amoeba- 

 fashion, or into a food-vacuole, or by a definite mouth ; 2 while 

 others, owing to the possession of coloured plastids or chromato- 

 phores, which may be green, brown, or yellow, are able to manu- 

 facture their own food-supply, after the manner of plants. 3 Again, 

 there are some species which, while possessing these chromato- 

 phores at one stage of their life, lack them at another ; or, as in 

 the case of Euglena, an organism common in fresh-water pools, to 

 which, owing to its presence in vast numbers, it often imparts a 

 greenish hue, the same individual may combine the characteristic- 

 ally animal (holozoic) with the typically vegetable (holophytic) 

 mode of nutrition, during the course of its life. 



The Euglena has a spindle-shaped body, with, at the blunt 

 end, a depression or gullet, from the inner surface of which arises 

 a long flagellum used for locomotion. The greater part of this 

 microscopic organism is green in colour, due to the presence of 

 the characteristic vegetable pigment, chlorophyll, and contains 

 grains of a carbohydrate allied to starch, called paramylum. A 

 bright red speck of pigment is also noticeable, which is thought 

 probably to function as a light-perceiving organ, a sort of very 

 rudimentary eye. The whole body is invested by a very thin 

 skin, or cuticle, so that, though the Euglena does go through cer- 

 tain worm-like movements of expansion and contraction, it is 

 incapable of the free and ever-changing pseudopodial movements 

 of amoeba. By means of its chlorophyll the Euglena is able to 

 decompose the carbon dioxide of the air dissolved in the water 

 of the pool in which it is living, and, by assimilating the carbon, 



1 The Saprophytic method of feeding, which is also characteristic of certain fungi. 



8 Holozoic. 



8 Holophytic. It is by means of the microscopic green chlorophyll-bodies or 

 plastids that the higher plants, under the influence of sunlight, manufacture their 

 food-supply, drawing the carbon dioxide from the air. 



