LIMNOCODIUM IN THE UNITED STATES. 3 I 3 



long and usually extended upward over the bell in graceful 

 curves ; other tentacles in several cycles, the newer arising along 

 the inner edge of the margin ; the older ones set in notch-like 

 scallops about the margin, as shown in Fig. 5. The general 

 color of the bell translucent, or of faintly bluish tint by reflected 

 light. Bases of tentacles surrounded by a dull brownish, but in- 

 conspicuous pigment. 



Experimental. 



The extensive experimental work which has been done upon 

 medusae within recent years, and the various results which have 

 been obtained by different experimenters, at once suggested the 

 desirability of repeating certain phases of it upon a fresh-water 

 medusa. Accordingly I devised a series of experiments to test 

 its regenerative capacity along lines similar to those made by the 

 writer on Gonionemus, Rhizostoma and others ; to test its behavior 

 in response to various stimuli — photic, chemical, mechanical, 

 tactile, etc. Having received less than a dozen living specimens 

 in the first lot it was of course out of the question to set about 

 any systematic and extended experimentation at that time, 

 fully anticipating ample material later for the work planned. As 

 already intimated in the introduction, these plans were doomed 

 to miscarry, owing to the utter failure in securing the necessary 

 material for their realization, and but for a single series of very 

 simple experiments this feature of the work would have been 

 wholly lacking. The experiments alluded to had to do wholly 

 with the reaction of the medusae to distilled water. 



The numerous experiments to determine the role of certain 

 salts in relation to the rhythmic movements of medusae are too 

 well known to call for extended review. On the one hand it is 

 claimed that the presence of certain ions (Na), is the all-important 

 factor in arousing and sustaining the movements, while the pres- 

 ence of certain other ions (Ca, K), have an inhibitory effect upon 

 them. " Na ions start or increase the rate of spontaneous rhyth- 

 mical contractions ; Ca ions diminish the rate or inhibit such 

 contractions altogether." 



On the other hand it has been claimed that Mg ions are the 

 magic factor which causes the organism to perform its rhythmic 



