Il] FLAGELLATA 33 



and contracts it till it is almost spherical. The peculiar wriggling 

 movements which it thus executes are so unlike anything else that 

 they have been called euglenoid. The reason for their possibility 

 is that the cuticle is flexible and that the outermost layer of the 

 protoplasm contains differentiated threads termed myonemes 

 which have special powers of contractility. An ectoplasm possessing 

 permanent elements like this is spoken of as a cortical layer. 

 The other peculiarity is still more striking, and it is that the proto- 

 plasm is coloured bright green and that it contains particles of a 

 substance very like starch. Now this indicates that Euglena feeds 

 itself like a plant, and that it constructs its protoplasm out of 

 carbon dioxide and mineral salts dissolved in water in the presence 

 of sunlight. The only points therefore that can be suggested in 

 which it differs from plants are that it has a flagellum and moves, 

 and that it does not possess a covering of cellulose. These supposed 

 differences, however, will not stand examination; the germs of 

 many undoubted plants, such as, for instance, the sea-weeds, have 

 no cell wall and propel themselves by means of flagella. What 

 justification then, it may be asked, have we for reckoning Euglena 

 as an animal ? What do we mean by so classing it ? It must 

 indeed be admitted that when we come to deal with the simple 

 Flagellata, the animal and plant kingdoms merge into one another, 

 and the only valid line of division we can draw is between forms 

 which feed on solid food, and those which absorb dissolved nutri- 

 ment; and amongst the latter we call those forms animals which 

 we believe to have been derived from ancestors which fed on solid 

 food. Now the pharynx in Euglena takes in solid particles from 

 time to time and these passing into the protoplasm are apparently 

 digested. We might therefore imagine either that Euglena is a 

 plant which has acquired a pharynx and is commencing to live like 

 an animal or else that it is an animal that has acquired chlorophyll 

 and has commenced to live like a plant. The fact that the pharynx 

 is small and of little use is against the idea that it is an organ 

 which has been newly acquired as all organs are acquired on 

 account of its usefulness. It has the appearance of being the 

 vestige of a once useful organ and therefore we conclude that 

 Euglena is an animal which has begun to live like a plant. 



The reproduction of Eugkna and of the Flagellata in general is 

 effected by longitudinal division whilst they are moving about, 

 but they also divide by transverse fission when in an encysted con- 

 dition into two or four, or a larger number of germs; these germs 



S. & M. 3 



