472 ME. HAEOLD WAGEE OIT THE 



the motile cells of Fucacese * and Algge f, is dou^btful. The 

 breabing-up of the eye-spot which has been observed in old 

 encysted cells may simply be a part of the general disintegration 

 of the cell; if not, it would appear that a new formation of 

 the eye-spot must take place on the resumption of the motile 

 condition. This, however, requires further investigation. 



Without entering into any further discussion of these facts, 

 it is clear, I think, that the eye-spot is a definite organ of the 

 cell possessing a characteristic, but simple structure ; that it is 

 probably a derivative of chlorophyll ; that it is present in the 

 motile cells only of those Algse in which it has been described and 

 is formed de novo when they are produced ; and that even in Eu- 

 glena, although it is present both in the motile and in the resting 

 condition, it disappears, or becomes broken up, in cells which 

 remain long in the encysted condition. We are probably justified, 

 therefore, in concluding that the eye-spot is an organ of the 

 motile stage of both animal and plant cells, specially connected 

 with their power of movement. 



The Flagelluon. 



The flagellum is an organ of the cell especially connected with 

 its rapid movement through the water. If it is absent, the 

 Euglena is only capable of a slow creeping movement which is 

 caused by a peculiar contraction of the body, characteristic of 

 the organism. This contraction appears to originate in the 

 protoplasm, but the different forms assumed are probably to 

 some extent dependent upon the elasticity of the limiting layer 

 or cell-wall ; and Khawkine (Z. c.) suggests that contractile fibres 

 are present — longitudinal ones over the whole of the cell, and 

 transverse ones in the anterior region only. These, however, 

 have not yet been seen, the only indication of any such contractile 

 fibres being the oblique strige found on the cell-wall ; and so far 

 we have no evidence that these play any part in causing the 

 contraction of the cell. 



The free movement of the cell through the water is entirely 

 due to the flagellum, which by its rapid motion draws the cell 

 after it, causing it at the same time to rotate around its longi- 

 tudinal axis. Very little is known of the actual mechanical 

 means by which this is accomplished, but an interesting discussion 



* Guignard, I. c. t Overton, I. c, and Johnson, I. c 



