1902,] NATURAL SCIENCES OF PHILADELPHIA. 17 



at frequent intervals. As stated above, Stenophora is so large that 

 it is impossible to keep both the protomerite and the upper surface 

 of the deutomerite in focus at the same time. But gregarines 

 which showed these slight displacements of the protomerite were 

 ^ displa}dng the typical gliding movement, and such gregarines 

 usually show the transverse movement. Moreover, by transferring 

 the attention from the upper surface of the deutomerite to the pro- 

 tomerite, it was possible to see that both of these two sorts of move- 

 ment take place at only very slightly separated periods of time. 



It is evident that lateral movements of the protomerite which are 

 at all e\'ident must take place in a horizontal plane. A movement 

 in a vertical plane would need to be far more extensive in order to 

 be detected. Vertical displacements, however, can often be seen. 

 That is, gliding gregarines move the protomerite indifferently in 

 any direction. This appears to me a fact of considerable signifi- 

 cance. It indicates that bendings of the protomerite may take 

 place even when it is not possible to see them. Fig. 13 is a dia- 

 gram of the anterior part of a gregarine. The solid line represents 

 the longitudinal axis. The dotted line represents the axis of the 

 protomerite when displaced in a horizontal plane. This displace- 

 ment is so slight that it is clear, were it to be effected in a vertical 

 plane, the highest powers and the most rigid attention would wholly 

 fail to detect it. 



It therefore seems reasonable to suppose that the transverse move- 

 ment is dii'ectly correlated with either displacements of the pro- 

 tomerite or bendings of the body in the region of the septum. 

 When both are extensive the connection is readily established, but 

 when the transverse movement is slight, this can only be done by 

 somewhat indirect means, as I have just pointed out. Yet it would 

 be improbable that the transverse movement should at one time be 

 correlated with bendings of the anterior part of the body, and not 

 at other times, when the difference in the two cases is merelv one of 

 degree. 



If, as I hope, my conclusions are warranted by the observational 

 data, the cause for gregarine progression is extremely simple, and 

 while the exact mechanics of the process are probably bevond 

 observation, it may be suggested that it is effected in a manner 

 somewhat as follows: The muscular impulse, starting backward 

 from the region of the septum, necessarily causes the contact of the 



