1902.] NATURAL SCIENCES OF PHILADELPHIA. 9 



glide forward without auy alteration in the body form, and this is 

 frequently the appearance. The converse statement, that gliding 

 takes place while the animals are displaying evident muscular con- 

 tractions, has never, to my knowledge, been made, although the 

 fact itself can scarcely have escaped frequent observation. Yet 

 progression without alteration in the outline of the body is no more 

 frequently seen than progression accompanied by obvious muscular 

 contractions. Gregarines may also progress, in either a straight 

 line or in zigzags, with the body held rigidly in a contorted form. 

 My observations here differ from those of Schewiakoff. On p. 348 

 he says that progressing gregarines may alter the direction of their 

 progression, and continues : "In solchen Fallen bemerkt man jedes 

 Mai, wenn die Bewegimgsrichtung verandert Avird, dass an der 



einen Seite der Gregarine eine Querfalte auftritt Die 



Gregarine wird aus der friiheren Bewegungsrichtung nach der Seite 

 hin abgelenkt, auf welcher die EinschniJrung am Gregarinenkorper 

 erfolgte. Bleibt die Einschniirung liingere Zeit hindurch bestehen, 

 so wird die Bewegung bogenformig, ja sie kann sogar zu einer 

 spiraligen oder schleifenformigen werden. Wird die Einsch- 

 niirung auf gehoben, d. h., die Gregarine wieder gerade gestreckt, 

 so wird die Bewegung von Neuem geradlinig." He believes that 

 the bending of the body is the cause of the turning. For when 

 the body is bent, the extrusion of the gelatinous fibres from the 

 bent side is hindered. The residt is a weakening of the propelling 

 force on the bent side, with the natural result of a turning to that 

 side. Straightening of the body brings about a uniform protrusion 

 of the gelatinous fibres on all sides, with a resumption of progres- 

 sion in a straight line. 



According to my observations, however, it is impossible to estab- 

 lish any definite correlation between alterations in the direction of 

 progression and extensive muscular contractions. The animals 

 may turn without the slightest bending of the body. As Sche- 

 wiakoff says, they may turn and bend to the same side, but, on 

 the contrary, they frequently turn lo one side and bend to the other. 

 Further, they may progress in a straight line with the body held 

 rigidly in a contorted form, as stated above. 



Progressing gregarines, without their progression being in any 

 ways checked, will often bend and suddenly straighten with a jerk. 

 This movement may take place a number of times and it has a 



