3 oo SCIENCE PROGRESS 



nourished by the decomposition of carbon dioxide and also by 

 the absorption of dissolved organic matter. It is doubtful 

 whether solid particles are taken in and digested. 



Euglena abounds in farmyards, where it forms a bright 

 green scum on the surface of dirty pools ; it is also plentiful 

 on sewage-farms. 1 



Like Chlamydomonas, Euglena is attracted towards a source 

 of light. If a little mud containing this organism be put into 

 a saucer of water and set in a good light, the green cells slowly 

 emerge, forming at first a green film which overspreads the 

 surface but afterwards rises through the water towards the 

 light. When shaded, they begin to sink, arranging themselves 

 at the same time in a network (fig. i); it is enough to bring 

 the hand between them and the light to set up these changes. 

 Remove the hand and they move upwards towards the light, 

 while the network disappears. In a strong light, which strikes 

 the surface of the water obliquely, the Euglenae form streaks 

 more or less parallel to the rays ; if the light be weak, the 

 streaks are transverse. When placed in a glass vessel exposed 

 to a strong light, the cells cluster on the best-illuminated side 

 of the vessel and form a green line at the water's edge. From 

 such a green line or any mass of Euglenae floating at the 

 surface, streams of cells may be seen descending into the liquid 

 and gradually becoming disseminated through it. Being thus 

 brought out of the shadow of the mass and into the path of 

 the light-rays, they begin to ascend again and to seek the 

 illuminated side of the vessel. A continuous circulation is 

 thus kept up and the Euglenae are prevented from too dense 

 an aggregation, which would interfere with their assimilating 

 and respiratory functions. Screen the vessel by a sheet of 

 card and a downward movement becomes more decided, the 

 Euglenae disappear from the surface and the upper layer of 

 the water becomes clear. If the vessel be kept in the dark 

 the Euglenae remain in constant movement, forming an irre- 

 gular, diffused network which extends through half an inch 

 or three-quarters of an inch of depth measured from the bottom 



1 Our limits of space preclude the possibility ot discussing the life-history 

 of Euglena at length. Some information concerning the encysted resting-stage, 

 the means of dispersal and the behaviour of Euglena; in the presence of adverse 

 conditions, such as drought or the attacks of parasites, will be found in the original 

 memoir (Wager, Phil, Trans, B, vol. 201). 



