DEPARTMENT OF MARINE BIOLOGY. 163 



conclusions are explainable (in part at least) upon other grounds than he 

 assumes, and because results of the type he secured are obtainable when fishes 

 are stained and fed as he fed them, but without Cassiopea stings at any stage 

 in the experiment. 



It is clear, therefore, that although a promising beginning has been made, 

 much that is interesting remains to be discovered regarding the powers of 

 discrimination and association in the gray snapper. 



Investigations at Tortugas, by Asa A. Schaeffer. 

 Distribution of Marine Amebas in Surface Water, Beach Sand, etc. 



The method of determining the distribution of bacteria-feeding amebas 

 belonging to the genus Flabellula, which was devised and tested in a pre- 

 liminary way in 1922, was given a more thorough test this season. Thanks 

 to the unusually ample and efficient aid by the members of the crew, a much 

 larger number of tests were made than would otherwise have been possible. 

 In all, 1,016 cultures were set up and examined, including in this number 12 

 controls. Following is a synopsis of the experiments: 



Experiment 1, June 8. — Wet beach sand, over a circular area of 594 sq, cm. 

 and to a depth of 7 cm., was collected a meter below high-tide line and close 

 to the water's edge during a falling tide on the northeast end of Loggerhead 

 Key. The sand was gently washed with 10 liters of clear sea-water dipped 

 up in sterilized vessels a short distance from the dock. The water was then 

 drained off and placed in 101 sterilized 100 c.c. bottles, a small piece of auto- 

 claved Sargassum was placed in each bottle, and the bottles were closed with 

 the sterilized cotton plug. The bottles were then set aside for 9 to 11 days 

 and examined for amebas. From 3 to 15 minutes were spent on each 

 bottle, usually the shorter period, to note the presence of Flabellula mira 

 and F. citata particularly, but the presence of other species of amebas was 

 also noted, as well as the presence of ciliates of whatever species and of large 

 flagellates. (As the purpose of these experiments was to test the presence 

 of the most widely distributed marine amebas, Flabellula mira and F. citata, 

 no time was taken to positively identify other species of protozoa.) Of the 

 101 bottles in this experiment, 47 contained amebas, 61 contained ciliates, 

 7 flagellates, while 36 bottles contained Flabellula mira, and 6 F. citata. 



Experiment 2, June 12. — An hour after low tide, 101 bottles were filled 

 with water from the moat at the fort, as far as possible from the moat opening. 

 The bottles were supplied with Sargassum, as in the previous experiment, and 

 then set aside for 10 days. Results of the examination are tabulated below. 



Experiment 3, June 12. — At a point in the lagoon a few hundred meters 

 west of the moat-opening of the fort, 104 bottles were filled with surface 

 water and supplied with Sargassuyn and set aside for 11 days. The results 

 of the examination are tabulated below. 



Experiment 4, June 22. — A pit was dug in the sand in the northeast end 

 of Loggerhead Key, among bushes of Bay Cedar and Tournefortia, a few 

 centimeters below the water-level at low tide. Care was taken not to let any 

 of the vegetable mold, debris, and sand of the surface fall into the pit. The 

 sand had apparently been undisturbed for a number of years. Of the water 

 which collected in the pit, 104 bottles were filled and treated as in the other 

 experiments. The examination at the end of 10 days' incubation gave the 

 results shown below in the table. 



