336 PROCEEDINGS OF THE SOCIETY. 



be equalled, even in these days, and he would have great pleasure in 

 exhibiting them to the Society on some future occasion. 



The vote of thanks to Mr. Heron-Allen for his exhi1)ition was 

 carried with acclamation. 



The Chairman then announced that the exhibit contributed by the 

 Biological Section in connexion with high-power dark-ground illumina- 

 tion would be introduced by Mr. Scourfield. 



Mr. Scourfield, dealing with the application of high-power dark- 

 ground illumination to the study of locomotion in flagellate organisms, 

 pointed out that most of the current theories put forward in reference 

 to this phenomenon were based upon inference only, since, owing to the 

 extreme rapidity of flagellar movements, direct observation was prac- 

 tically impossible. The generally accepted theory advocated by Biitschli 

 was, that the flagellum acted like a rotating screw, either in front or 

 behind the organism ; but Ulehla's recent investigations under high- 

 power dark-ground illumination showed that the theory was untenable 

 in many cases, since the space covered by the flagellum when in normal 

 motion (called the " light space," because it became illuminated under 

 dark-ground conditions), could not be produced by a screwing motion — 

 in certain forms, such as Monas, etc., the light space did not correspond 

 in the least to any rotation figure, because in one view it was merely a 

 curved line, while in the view at right angles to the first it was more or 

 less oval. Further, in many instances {Bodo^ EugJena,, TracheJomonas, 

 etc.), the active flagellum was held at right angles to the organism, and 

 yet the animal went strai,i(ht forward. In biflagellate organisms like- 

 wise, he found that the flagella stood out at right angles, and obviously 

 a screw acting in one direction could not produce locomotion at right 

 angles to that direction. Thus, instead of the movement of flagella 

 being a question of continuous spiral wave-motion, the action was prob- 

 ably in reality a series of beats or strokes. 



More investigation, was, however, necessary, and high-power dark- 

 ground illumination enabled the actions of flagella to ])e studied from a 

 new point of view. Mr. Scourfield said that he had to some extent 

 been able to confirm Ulehla's results. 



Mr. Blood asked whether the motion of flagella could , be sloAved 

 down by mucilage in the water, or otherwise. 



Mr. Scourfield replied that when a flagellum was artificially slowed 

 down its actions and position might be so altered that a fallacious con- 

 ception of the flagellum in normal action might arise. 



The Chairman regretted tliat owing to failure of the electrical 

 arrangements, he could only refer to the Abbe " Demonstration Micro- 

 scope," on the stage of which there was a grating. The grating was 

 illuminated by means of a collimator, with a slit at one end, and was so 

 arranged that an image could be obtained of the posterior focal plane of 

 the objective, showing, at will, the diffraction spectra formed by the 

 grating, or a real image of the grating itself. By suppressing the zero 

 maximum diffraction spectrum and decentring the illuminating slit, 



