ON THE SPECIFIC GRAVITY OF SPIROSTOMUM, 
PARAMA:CIUM, AND THE TADPOLE IN 
RELATION TO THE PROBLEM 
OF GEOTAXIS! 
JULIA B. PLATT. 
Ir is known that some algz and Infusoria tend to collect 
near the surface of the water in which they live. A number 
of experiments have been made which seem to demonstrate 
that the tendency thus manifest cannot be ascribed altogether 
to the attraction of light, or to the source of oxygen supply, 
since these algze and Infusoria still move upwards when the 
experimental conditions are such as destroy or reverse the 
normal relations to air and light. It is, therefore, affirmed 
that these organisms react to the force of gravity. This 
reaction, or negative geotaxis, is attributed by Schwarz (84) to 
the direct influence of gravity on the organism, which incites 
motion in the opposed direction, while Jensen ('93) attributes 
the reaction to the indirect influence of gravity on the organism 
by means of the difference in hydrostatic pressure at different 
depths, The experiments of these authors seem to show that 
the possibly excentric position of the center of gravity in the 
organism cannot be regarded as a factor one the direc- 
tion of motion. 
Dr. C. B. Davenport suggested that a simple and hitherto 
unrecorded method of approaching the problem of geotaxis 
might be by means of solutions of varying density in which 
the infusorian would still live. Obviously, if the conclusion 
of Schwarz (84) were right, the negatively geotactic organism 
should become positively geotactic in solutions of greater spe- 
cific gravity than its own, supposing the animal to be normally 
heavier than water. 
1 This short study was undertaken as laboratory work in connection with 
Dr. C. B. Davenport’s course in Experimental Morphology. My cordial thanks 
are due Dr. Davenport for the kind interest with which he followed the work. 
31 
