NEMATOCYSTS OF MICROSTOMA. 247 



the green protoplasmic mass of the Hydra's body and retain 

 the nematocysts within its enteron. This does not appear to 

 be due to the fact that the pressure has held fast the mass of 

 nematocysts ; for, during the process of egesting the other Hydra 

 material, the nematocysts are being thrust to and fro within the 

 enteron. Under such condition a Microstoma, therefore, re- 

 jects the food and retains the nematocysts. 



Microstoma MAY EGEST NEMATOCYSTS AND RETAIN CELLS 



OF Hydra. 



The senior author saw just the reverse of this. A Microstoma 

 was loaded with nematocysts by being fed a Hydra. It was 

 then starved until it would accept Hydra. While the Micro- 

 stoma was kept under observation the Hydra was digested. 

 When alimentation had been completed the indigestible nemato- 

 cysts were thrown out of the mouth and rejected. When Dr. 

 W. H. Taliaferro, now of Johns Hopkins University, was told 

 this he expressed skepticism ; his challenge was accepted by the 

 senior author to have this demonstrated. From 10.58 A.M. 

 to 11.14 A.M., September 19, 1917, Dr. Taliaferro kept the 

 " loaded " Microstoma under observation. During this time he 

 could see the nematocysts of a recently ingested Hydra within 

 the enteron. At 11.14 A. M., he saw the nematocysts being dis- 

 charged from the mouth of the " loaded " Microstoma. 



From these observations it appears, therefore, that Hydra is 

 eaten by Microstoma not primarily as a food but for its nema- 

 tocysts. Thus, it is further suggested that the handling of the 

 nematocysts by Microstoma is done in order that the rhabdo- 

 coele may use these " stinging threads." 



DISCHARGE OF NEMATOCYSTS BY MICROSTOMA A DOUBLE 



PROCESS. 



When one teases a Microstoma, that is armed with Hydra's 

 nematocyst, the nematocyst in the immediate neighborhood of 

 the stimulus oscillates to and fro at right angles to the surface 

 of the body. If the teasing is maintained long enough, the nema- 

 tocyst will be discharged at the object with which the Microstoma 



