406 GUSTAF FR. GOTHLIN 
tal position. They were then, as far as I could see, without excep- 
tion oriented in such a way that the meridian line, which goes 
through the points of the two polar fields, was situated horizon- 
tally. This position, to which [ shall have to return several times 
in my accounts of the experiments, is there called ‘the usual hori- 
zontal position.’ In this position the animals glided along the 
bottom of the aquarium. At the corners of the aquarium they 
remained sometimes stationary for hours in full ciliary activity. 
They sometimes made short excursions up to the higher layers of 
the liquid. On the other hand, they did not, as a rule, remain at 
the surface of the liquid for any length of time when they were in 
good condition. I only observed in two cases in my experi- 
mental animals a vertical position, described by Verwern (91, pp. 
443-446, 451) as common, with the mouth facing upward toward 
the free surface of the liquid. 
As the condition of the animals obviously deteriorated with 
warmth, the majority of the experiments were carried out in the 
aquarium room at the station, where the temperature was almost 
always below 20°. During the time of observation and especially 
when an electric current was used, the animals were kept in a 
cuvette with parallel walls of mirror glass. The cuvette, to 
which they must be transferred very cautiously, measured inter- 
nally 30 mm. in width, 110 mm. in length, and 110 mm. in 
height. The longitudinal axis of the animal was placed in the 
longitudinal axis of the cuvette and the meridional rows were 
observed from the side with a Briickes lens mounted oni a stand. 
The magnification was 8 times and the background was the open 
sky. In counting the number of ciliary waves during a certain 
time a stop-watch and the lens were used. 
In the experiments with electric currents the electrodes con- 
sisted of two glass tubes 20 mm. in diameter, the lower ends of 
which were ground obliquely. The tubes were filled up at the 
bottom to a height of about 3 em. with a dough made by knead- 
ing together powdered clay and sea-water. At the bottom the 
free surface of the clay was fastened over with a piece of chemi- 
cally clean gauze. In the tube, above the layer of clay, there was 
a saturated solution of zine sulphate up to a height which, when 
