NEMATOCYSTS OF MICROSTOMA. 243 



cysts out from their anchorage within the worm's body and 

 then glided along the right side of the body posteriorly to 

 where it fused with the posterior mass, which had three nemato- 

 cysts enclosed within it. This compound mass of mucus, now 

 containing five freed nematocysts, was sloughed off from the 

 Microstoma's body and left behind. After that the Microstoma 

 seemed to be enveloped in a transparent mucus sheath to which 

 small dead objects adhered and were dragged about with the 

 Microstoma until they became entangled with the tentacles of 

 the Hydra. These tentacles stripped the foreign bodies from the 

 Microstoma's adhesive surface. Another observation of this 

 sort was made January 29, 1917. A Microstoma was placed 

 with a large budding Hydra fusca. It at once attacked the 

 Hydra. The Hydra discharged a nematocyst into the anterior 

 end of Microstoma. The Microstoma contracted so vigorously 

 as to break apart the two nearly formed zooids that had been 

 developing through fission. About the deeply anchored nemato- 

 cyst the anterior zooid now secreted a local mass of mucus. 

 This mass of mucus grew until it formed a column whose length 

 was more than two-thirds that of the zooid. Next the posterior 

 zooid encountered the bud of the Hydra. As it passed the 

 Hydra, the latter stung it in its posterior end along the left 

 side. About this nematocyst a local secretion of mucus appeared 

 and as the mass of mucus grew in length the long stinging 

 thread of the nematocyst was dragged from the Microstoma's 

 body as had a mucous column dragged the nematocyst from 

 the body of the anterior zooid. Eventually the mucous masses 

 were discarded and the two zooids appeared to be no worse 

 for their experience. 



All the above shows an intimate relation existing between 

 Microstoma and Hydra which is peculiar and must have some 

 meaning while much of the above indicates that the meaning 

 of this conduct centers about the nematocysts of Hydra. 



Microstoma WITH FEW NEMATOCYSTS REACTS TO Hydra 



READILY. 



Moreover, a Micwstoma that has few or no nematocysts be- 

 haves differently towards Hydra than does one that has a com- 

 17 



