82 POTTS: A FRESH WATER JELLY FISH. 



When comparing the two medusoids, Figures i and 2, said 

 to have been found in swarms, it will be instructive to observe 

 that both seem to have grown in quiet waters ; while Micro- 

 hydra passed its earlier stages in rapidly flowing, sometimes 

 deep currents. It may be supposed, therefore, that these dif- 

 ferent conditions promote the frequency of one or the other of 

 the described modes of reproduction, and help to explain the 

 fact that even after twelve ^-ears of study the wediisoid of the 

 last was only found in the artificial condition of m}' culture- 

 jars and that it has never been seen either in Creek or Canal. 



In conclusion I take pleasure in acknowledging the cour- 

 tesy always shown me by Dr. E. Ray Lankester, by reprinting 

 here the note that he appended to my original article : — 



" Mr. Potts has been so very kind as to send to me, at my 

 request, a specimen of the minute medusa liberated by Micro- 

 hydra and preserved in formalin. It is one of two which 

 remained in his possession. Whilst further study of Micro- 

 hydra and its medusa is urgently called for, it is clear that 

 further research is needed in order to settle the doubt enter- 

 tained by Mr. Potts as to the actual genetic connection of 

 Bourne's hydroid with the medusa Limnocodiiim . It is within 

 the bounds of possibility that that h^^droid is a native European 

 polyp, similar to Microhydra, and not connected with the 

 Limnocodiiim \\{it-c\c\Q^." 



