312 WM. A. KEPNER AND FRANK HELVESTINE, JR. 



That Microstoma can come up and tear off a tentacle of Hydra 

 without the other tentacles or any other parts of the victim's 

 body being disturbed has been frequently observed in this labora- 

 tory. When the entire Hydra is being ingested, the body of the 

 prey contracts to a form shown by contour A, figure 8. Some- 

 times a Hydra that has been thus ingested is egested. Such a 

 rejected polyp remains quiet, neither expanding nor further con- 

 tracting, as if both its superficial or longitudinal muscles and its 

 deeper or circular muscles had been paralyzed. This condition 

 of complete paralysis is passed within an hour. Within that 

 period the recovery is complete. An interesting observation in 

 one case showed that the longitudinal muscles were not completely 

 paralyzed. For in this case, throughout the process of ingestion 

 the Hydra has a shape approximately like that indicated by con- 

 tour A, figure 8. As soon, however, as the polyp was crowded 

 into the enteron by the side of an oligochaete, that had been pre- 

 viously ingested by the Microstoma, it became spherical. Here, 

 then, the longitudinal muscles had the power to contract further 

 when they were more severely stimulated by the secretions of 

 the enteron. The partial paralysis of an animal ingested is 

 local and confined to the part of the body which has been taken 

 into the pharynx. That this is the case is indicated by a second 

 observation. A Microstoma was ingesting a Hydra from its 

 aboral end. The polyp, during the process, had a shape indicated 

 by contour A, figure 8. The rhabdocoele gave up and left its 

 prey after having held the aboral half of the Hydra in its pharynx 

 for nearly a half-hour. The Hydra, after being egested, showed 

 the power to move and to elongate only the oral half of its body. 

 For nearly an hour the oral end would elongate, ply to and fro, 

 contract and expand again; but through all of this activity the 

 aboral end that had been ingested remained quiet, so that the 

 Hydra, when its oral half was distended, had the form indicated 

 by contour B in figure 8. Here it is apparent that the paralyzing 

 effect of Microstoma had influenced the deeper or circular mus- 

 cles of Hydra's body. Thus it is indicated that both the outer 

 (longitudinal) and the inner (circular) muscles of Hydra are para- 

 lyzed by an attack from Microstoma, if it be sustained long 



