248 VVM. A. KEPNER AND JOHN F. BARKER. 



was being touched. An observer cannot watch this double re- 

 action on the part of the Microstoma when being stroked with 

 a needle point without feeling that the first phase of reaction, 

 viz., the oscillation of the nematocyst, is a threat and that the 

 second phase of the reaction, viz., the discharge of the nemato- 

 cyst, was an effort to use the nematocyst against the annoying 

 object. 



Microstoma USES ITS NEMATOCYSTS. 



Finally we have been able to see Microstoma actually using 

 the nematocysts that it had appropriated from Hydra. 



October 13, 1917, the senior author placed some Stenostomas 

 in a hanging drop with a Microstoma that had nematocysts. 

 One of the Stenostomas was at once stung along its side. The 

 wound caused the Stenostoma's body to rupture. After the 

 Microstoma had thus wounded the victim, it at once swallowed 

 it. Mr. Conway Zirkle saw this same Microstoma strike another 

 Stenostoma in such fashion as to cause it to bend its body near 

 the middle at right angles and to remain quiet in this contour 

 until the Microstoma fell to ingesting it. In neither of these 

 observations were the actual nematocysts seen entering or having 

 entered the Stenostoma. 



But on September 9, 1917, the senior author placed a large 

 Microstoma, containing nematocysts, in a hanging drop of water 

 with three very large dividing Stenostomas. The head of one 

 of these Stenostomas came in contact with the right side of the 

 Microstoma s head. Forthwith the Stenostoma contracted vio- 

 lently. From a wound at the tip of the body the mesenchyme 

 oozed. As this material ran out of the body, it dragged with it 

 two nematocysts that had their filaments and barbs ejected. The 

 Stenostoma's body also developed a small blister to the left of 

 the ruptured region of the epidermis. The Microstoma left the 

 Stenostoma, which no longer moved from place to place, and 

 later came back and attempted to ingest the Stenostoma as it 

 lay struggling as though suffering from its wound. 



September 19, 1917, the senior author placed a Microstoma, 

 that had nematocysts, in a hanging drop of water with a single 

 dividing Stenostoma. Eight times these two animals collided. 



