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 motive 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. 1 



II. 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, 



i Part I, p. 155. 



