On the Nervous System of Cassiopea Xamachana. 125 



TECHNIQUE OF THE EXPERIMENTS AND SOME RESULTS OF OPERA- 

 TIONS THAT APPLY EQUALLY TO ALL EXPERIMENTS. 



The natural habitat of Cassiopea is in shallow lagoons, usually in 

 areas where mangroves are abundant, where the water is daily subjected 

 to marked fluctuations in temperature, and where the salinity is most 

 affected by precipitation. In such locations, many of which are 

 practically stagnant, the variations in salinity are of wide range, as 

 evaporation is rapid during the summer months, when also the precipi- 

 tation is greatest. Such lagoons usually support an abundant algal 

 flora, so that the gaseous content of the water varies considerably and 

 large quantities of organic acids are continually being generated. The 

 environmental conditions consequently vary widely from time to time 

 and are always decidedly different from those in the open tropical ocean. 

 Indeed, so thoroughly inured to this environment is Cassiopea that it 

 thrives better under laboratory or lagoon conditions than in pure 

 sea-water. 



At Tortugas the proper environment for this form is restricted to 

 the moat, at Fort Jefferson, which is 50 feet wide, extends entirely 

 around the fort, and communicates with the open water outside at 

 only two points through narrow entrances which are entirely cut off 

 at extreme low tide. As the mean rise and fall of tides is in this region 

 only about 1.5 feet, the amount of change in the water of the moat is 

 slight and currents are scarcely detectable at a distance of 200 yards 

 from the entrances. Over the greater portion of the moat, the bottom 

 is densely covered with a mat of filamentous algae, while its side walls 

 furnish a place of attachment for innumerable specimens of hydroids, 

 bryozoa, tunicates, annelids, mollusks, and several species of corals. 

 Among the algae the cassiopeas lie on their aboral surfaces, with their 

 branching mouth-arms giving a flower-like appearance and with the 

 bell-margin pulsating slowly. In adult specimens, movement from 

 place to place by their own activity apparently occurs very rarely, 

 if at all. Even young medusae, not more than 2 cm. in diameter, 

 seldom are raised from the bottom by their own pulsation, and it is 

 doubtful if the larger specimens are capable of moving about by 

 swimming movements of the disk. 



The exumbrella surface is depressed in the center and can be used as 

 a sucking disk by which a medusa can attach itself firmly to a vertical 

 surface or resist removal from the bottom. This surface has a simple 

 layer of epithelial cells over the mesoglcea and is not provided with 

 either nerves or muscle-cells. 



When resting in its normal position on the bottom, the languid 

 pulsations of the bell-margin create currents sufficient to bring the food 

 material (which consists entirely of minute organisms) onto the mouth- 



