DEPARTMENT OF MARINE BIOLOGY. 



211 



between tide-levels the vessels would be filled and emptied through small glass 

 tubes by each rise and fall of the tide Avithout creating strong currents within the 

 vessel. One of these vessels was placed at the end of the wharf on the western 

 side of Loggerhead Key, where pure ocean-water might enter it. The other 

 vessel was placed in the moat at Fort Jefferson. When examined one year 

 later, it was found that in the vessel off the Loggerhead Key wharf a tunicate 

 Ciona had grown within the vessel, so as to stop the entrance and thus to 

 prevent the circulation of water. The bottom of this vessel was covered with 

 about 8 mm. of limestone mud which had been drawn in through the glass 

 tubes, and which gave off an odor of sulphureted hydrogen, but the water 

 within the vessel was inhabited by a number of marine animals, such as two 

 forms of Ciona, an Alpheus, and several worms and mollusks, all of which were 

 alive and seemed normal in appearance, and some of which had grown to be 

 too large to escape from the vessel through the glass tubes. The contained 

 shell was buried beneath the mud. 



The circulation in the vessel placed in the moat at Fort Jefferson was prop- 

 erly maintained and there was almost no mud in the bottom, so that the shell 

 remained surrounded by sea-water throughout the year. Carefully weighed 

 pieces of the Cassis shell were placed in each of these four vessels in July 1914 

 and removed in July 1915. The air temperature throughout the year ranged 

 from 15° to 37° C, the average being about 27°. The experiment shows that 



Rate of solution of pieces of Cassis shell in sea-water. 



*The balance was accurate to 0.001 gm. 



