GEOTROPISM IN PLANARIA MACULATA 



J. M. D. OLMSTED 



Contributions from the Zoological Laboratory of the Museum of Comparative 



Zoology at Harvard College 



No. 289 



Flat-worms, such as planarians, are commonly collected from 

 the underside of stones in a stream or pond (Bardeen, '01 ; Pearl, 

 '03; Whitehouse, '14). The resting position of these animals, 

 with their ventral surfaces uppermost, would seem to indicate 

 a negative response to gravity, since when moving they may 

 be in any position, depending upon the particular surface over 

 which they happen to be gliding. This investigation has as 

 its object the analysis of the resting behavior of these worms. 

 The specimens used were Planaria maculata Leidy and were 

 taken from Fresh Pond, Cambridge, Mass. A stock was brought 

 into the laboratory and kept in a large jar on a table about 

 four feet from a north window. 



To ascertain the relative importance of light and gravity in 

 the reactions to be studied, an experiment in the following form 

 was carried out. One-half of one surface of a glass plate, 10 x 

 8 cm., was coated with black wax. This plate was supported 

 in a horizontal position by wax feet 4 mm. high on a second 

 glass plate. The pair were placed in a flat dish and covered with 

 water to the depth of 3 cm. The flat dish had a collar of black 

 paper about its sides, so that only light from above could fall on 

 the plates. Then twenty planarians were placed at one time on 

 the upper plate, at another on the lower one, and their positions 

 recorded twice a day. As the animals moved about over the 

 whole dish for an hour or more after beginning the experiment, 

 the fact that they had started from the upper or lower plate 

 was not significant. 



The results of 30 readings showed that 30 per cent were not 

 under the plates, but usually in the shadow near the angle 

 between the bottom and side of the dish, 70 per cent being 



