233] STUDIES ON GREG ARINES —WATSON 23 



ersed often as great as the time it takes is short. The release may be com- 

 pared to the cutting of a tense cord. Generally, however, the parasite is 

 not able to effect its release and keeps on trying until the walls are rup- 

 tured or death ensues from some other cause. 



I have never observed backward gliding movement. The only back- 

 ward motion seen was the sudden jerking mentioned above. This phe- 

 nomenon may possibly be accounted for in the following manner : The 

 animal exerts considerable effort to move forward against the backward 

 pull of the threads and debris behind it. Its body becomes stretched out 

 long and narrow by the contraction of the myonemes. These myoneme 

 fibrillae suddenly relax and the body becomes shorter and normal in 

 shape. As the tension on the caudal threads is thus released, the body is 

 drawn backward with a sudden jerk. The motion is thus passive, a sim- 

 ple reaction and not actively incited motion in a backward direction. 



It is not to be denied, then, that there are formed gelatinous threads 

 which seem to fuse and form a thick thread or strand from the poste- 

 rior end of the body, but these threads are obviously an hindrance 

 rather than an incentive to progression. My theory concerning the rea- 

 son for the presence of such a group of threads will be discussed later. 



Granted here that such a group is present, it obviously comes from 

 the animal itself and is carried to the posterior end of the body by the 

 longitudinal ridges which gregarines possess (see Fig. 243 for illus- 

 tration of these longitudinal ridges). The animal in a mass of debris 

 tries to liberate itself. In this motion there is secreted a lubricating 

 substance which in a medium other than the normal digestive juices ad- 

 heres to the debris. In endeavoring to get free, a great deal of energy 

 is expended and considerable lubrication secreted; and thus the thread 

 is formed from which the animal is unable to extricate itself. Each 

 added trial only causes more secretion to be poured out and makes the 

 snare the more secure. The body becomes drawn out long and slender 

 indicating the strain which the animal undergoes (Fig. 236). 



I suggest the hypothesis that normally there is a secretion which 

 reaches the posterior end. When a parasite is moving through a me- 

 dium in which there is fine scattered debris, it picks up much of it. 

 After a considerable accumulation has taken place, one of two things 

 may happen: The end masses may drop off by their own weight, the 

 force exerted by the strand of threads being less than that exerted 

 either by the progressing animal or by the dead weight behind. If the 

 strand withstands the stress exerted by the moving animal but the dead 

 weight exerts greater force than the combination of the other two, the 

 strand and the animal, the parasite is caught and eventually dies. 



The presence of the caudal threads can often be demonstrated with 

 carmine. In a freshly made mount the carmine does not seem to adhere 



