1902,] NATURAL SCIENCES OF PHILADELPHIA. 11 



come to rest. But this does not happen. Such a turn as that 

 shown in fig. 3 may be a matter of only a second or two. 



Another case is shown in fig. 4, where a—f show six positions 

 successively occupied by a progressing gregarine. It is difficult to 

 see how the gelatinous stalk can explain a progi-essive movement of 

 this sort, which was seen a number of times. 



3. Schewiakoff arrived at his conclusions partly from a study of 

 the action of carmine particles, etc., in the vicinity of progressing 

 gregarines. Such particles are seen to slip backward along the 

 surface of the gregarine, and Schewiakoff believed they were being 

 pushed or carried backward by the extruding gelatinous substance. 

 He states that this take? place just before a gregarine begins to dis- 

 play a progressive movement, and continues during progression. 

 This is true, but these particles show such varied movements that it 

 is probable the extruding gelatin is not in all cases the cause. If 

 the extrusion of gelatinous fibres be the cause of gregarine progres- 

 sion, then the rate at which the gelatinous fibres are passed back- 

 ward should bear a direct ratio to the speed of the progressing 

 gregarine. The movement of the particles along the animal's sur- 

 face should mark the rate of extrusion, which shoidd itself condition 

 the rate of progression. But these particles may slip backward 

 either more rapidly or more slowly than the gregarine is progres- 

 sing. They may also slip rapidly backward along the surface of a 

 gregarine which is not changing place, and further remain at a fixed 

 point on the surface of a progressing individual. As a rule, the 

 slipping is seen in progressing animals, but often it is not. Fre- 

 quently a progressing individual causes little or no disturbance 

 among the loose particles lying in its path, merely pushing them 

 aside as it advances. The particles may also move forward along 

 the animal's surface. This is seldom seen in progressing grega- 

 rines, but is frequent in those which are displaying changes of body 

 form. 



The movements of these small particles are so multifarious as to 

 suggest that they are due to different causes. It is probable that 

 surface tension is in part responsible. At the same time, the evi- 

 dence that gregarines extrude a gelatinous substance is wholly con- 

 clusive. The animals are sticky, and will often remain adhering to 

 the cover-glass in spite of rapid currents in the mounting fluid. I 

 have also seen the substance arising from the surface of a progres- 



