178 STUDIES IN GENERAL PHYSIOLOGY 
Other conditions than light and gravity which might have 
influenced the perfectly vertical growth of the stem, or its 
geotropic bendings, when its position with reference to the 
vertical was altered, were shut out in these experiments. I 
was not able to make any experiments upon the centrifugal 
machine, as it takes some twenty-four hours to bring about 
the geotropic bendings, and because I could avail myself of 
no motivg power which ran uninterruptedly for so long a 
time. There can be no doubt, however, that we are dealing 
in this case with a geotropic phenomenon. 
There are, on the other hand, animals which are capable 
of geotropic curvatures through muscular contractions with- 
out any accompanying phenomena of growth. We find such 
conditions in an Actinian, Cerianthus membranaceus. This 
animal has the habit of burying itself vertically in the sand. 
If the animal is brought into any other orientation toward 
the vertical, it bends its body downward, beginning with the 
foot, until the entire animal has again a vertical position.' 
Il. GEOTROPISM IN FREE-SWIMMING ANIMALS AND _ ITS 
SIGNIFICANCE FOR THE BATHOMETRIC DISTRIBUTION OF 
CERTAIN PELAGIC ANIMALS 
1. Since the geotropic effects in the vegetable kingdom have 
been studied, in the main, only upon sessile organs, and are 
known in these only in the form of curvatures during growth, 
objection might perhaps be taken to the fact that I intend to 
speak of geotropism in free-swimming animals. But the 
term “geotropism” signifies only a dependence of the orien- 
tation upon gravitation, without saying anything concerning 
the mechanism of this dependence. It would therefore be 
mere pedantry if we should declare that such dependence 
could be designated geotropism only in sessile and not in 
motile animals. I will lose no time in arguing this question, 
1 Part I, p. 155. 
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