22 ILLINOIS BIOLOGICAL MONOGRAPHS [232 



Normal salt solution acts as a stimulant to motion and in it the para- 

 sites remain alive and active longer than in water. It is therefore the 

 best medium in which to observe motion. Sea water has practically the 

 same effect as normal saline. 



Movement of location consists of a uniform gliding progression with 

 no apparent localized motion of the body. It is best seen in animals from 

 a freshly opened host intestine mounted on a slide and supplied with an 

 abundance of light. The parasites are negatively heliotropie and conse- 

 quently attempt to avoid the light rays by moving rapidly from the tis- 

 sues toward the periphery of the cover slip and down the sides until they 

 encounter masses of debris under which they try to hide. 



The rate of progression has been measured in several instances. It 

 averaged 0,8 micron per second in Leidyana erraiica. The same individ- 

 ual is able to increase or decrease its rate of motion through a consider- 

 able range. A sample set of successive rates, measured at intervals of 15 

 seconds, reads as follows : 0.7, 1.8, 4, 5.6, 2.8, 1.5, 0.8, and 0.0 per second. 

 An accompanying diagram (Fig. 233) illustrates progression combined 

 with bending movement and the distances covered in successive time in- 

 tervals. In the Stenophoridae motion of progression is slower, an aver- 

 age being .007 per second for two species, one of which was five times the 

 length of the other and of correspondingly greater volume. 



Just how the progressive movement is effected is a matter much dis- 

 cussed. Schewiakoff (1894) makes the statement that it is caused by the 

 secretion of a hollow gelatinous ' ' stalk ' ' formed of contiguous threads at 

 the posterior end of the body which pushes the animal forward. He says 

 that the gregarine is able to move only until its store of secretion is ex- 

 hausted and cannot go on until it has accumulated the materials from 

 which to secrete a new addition to the ''stalk". 



Upon cutting off most of the light from the field, there can be seen 

 many fine threads leading from the posterior end of the gregarine back 

 to a mass of debris from which it is apparently trying to extricate itself. 

 A slight motion of the microscope or of the table beneath will cause the 

 threads to tremble ; but even a slight movement of the cover slip does not 

 rupture them. I have often observed the animal swinging about in an 

 arc at the end of this fastened thread or strand of threads without break- 

 ing it. This was noted in twenty-five instances in a single field and was 

 repeated by the parasites until their walls were ruptured and the proto- 

 plasm oozed out. 



After a mount has been made for some time and the gregarines have 

 become scattered about in the debris, many animals can often be seen 

 headed away from inert masses, moving a short distance forward and 

 then being jerked quickly back as if by some invisible spring. When an 

 animal is able to free itself, the relase is sudden and the distance trav- 



