6 PROCEEDINGS OF THE ACADEMY OF [Jan., 



of these two groups of organisms in that diatoms move indifferently 

 in two directions, whereas gregarines always move forward. But 

 in both cases the movement takes place without visible cause, and 

 when Lauterborn showed that diatoms progress by means of the 

 extrusion of threads of an invisible substance, a presumption was 

 established that the cause for gregarine progression was to be sought 

 for along similar lines. 



Accordingly, Schewiakoff undertook a study of living gregarines. 

 As mounting media, he employed either normal salt solution or 

 an albumin solution of the following formula : 



Egg-albumin, 20 cc. 



Distilled w^ater, 200 cc. 



Sodium chloride, 1 gi"* 



Powdered carmine, Chinese black and, in some cases, native sepia 

 were added to the fluid, so that invisible extrusions from the grega- 

 rines could be detected. 



The results were to show that gregarines usually caught up and 

 pulled after them a number of particles of carmine, etc., thus 

 demonstrating the presence of a sticky substance. Further, as a 

 gregarine progressed through a medium thickly filled with carmine 

 particles, there was always left behind it a clear trail. Schewiakoff 

 says that this does not happen with other Protozoa, and so furnishes 

 proof that gregarines leave something behind them. This substance 

 was wholly invisible under ordinary circumstances, but very delicate 

 manipulation enabled him to stain it and to demonstrate that grega- 

 rines actually are followed by long fibres of extreme tenuity. Stress 

 was laid upon the fact that carmine particles in the neighborhood 

 of a motionless gregarine could be seen to show molecular move- 

 ments ; next to slip backward along the surface of the animal and 

 to collect in a lump at the posterior end, and that only after this 

 had taken place would the animal progress. 



In the course of what follows, there will be frequent occasion to 

 refer to Schewiakoff' s statements, and the conclusions that he draws 

 from them, in much greater detail. I have given above only his 

 results, and a few of the more important observations upon which 

 these results were based. His explanation of the cause of gre- 

 garine progression has been accepted by most authors, yet in some 

 cases with a considerable amount of reserve. Lang (1901, p. 127) 

 and Doflein (1901, p. 161) accept it without comment. Calkins 



