COLE. — IMAGE-FORxMOG POWERS OF VARIOUS TYPES OF EYES. 365 



time. Bell ("86, p. lO.s) remarks that "There can be no doubt as to 

 the sensitiveness of Bipalium to light," but he referred only to what 

 he supposed was the eft'ect of strong light in causing the worm to break 

 up into a number of pieces, and not to the directive action of the light. 

 As a matter of fact, Bipalium hirense is exceedingly sensitive to light, 

 of even a very low intensity, falling upon it fr-om the side, and responds 

 immediately by turning away from the light. For this reason, and 

 because it is easy to keep and to handle, it is an excellent animal for 

 experimental purposes. Like most planarians, it creeps with an even, 

 gliding motion, the head being slightly raised and waved to right and 

 left, apparently in searching movements, as the worm crawls forward. 

 In the daytime this Bipalium is usually to be found coiled up under- 

 neath flower pots which sit on the ground in warm, moist rooms of 

 greenhouses ; and it is probable that it comes out and moves around 

 only at night. What it eats appears not to be known with certainty, 

 but the common opinion seems to be that, like other turbellarians, it is 

 carnivorous. Some of the related forms are known to eat earthworms, 

 and certain authors believe the same to be true of Bipalium Jceivense. 



Description of Experiments. The experiments on Bipalium were 

 conducted in the same manner as those on the earthworm, except that 

 the ground glass on which the animals were placed was supported 

 about 1 cm. above the table by means of small wooden blocks, or feet, 

 glued to the under surface of the glass at its four corners, instead of 

 being swung free by strings from the ceiling. By lifting the plate very 

 slightly, it could be turned easily in any direction. This had the ad- 

 vantage that when the worm was once in the proper position, the wooden 

 feet could be brought in contact with the table again, the plate thus re- 

 maining perfectly steady and horizontal. When the worm was creeping 

 well in the shaded area, the plate was moved so that about 5 mm. of 

 the anterior end of the worm was brought out, in the normal posi- 

 tion, into the influence of the light, and the record was taken when the 

 animal's head reached the fin^t circle, instead of the third, as in the 

 case of the earthworm. It thus crawled a distance of only 4.5 cm. at 

 each trial ; but the reactions of Bipalium are usually so immediate and 

 definite that this distance seemed sufficient for the purpose of the 

 experiment. 



The results of 10 trials each, with 10 worms (100 trials in all), when 

 both lights were operative, are shown in Table III. It will be noticed 

 that more than half of the 100 trials fall in the class, and that only 

 a single record falls more than two classes to right or left of that posi- 

 tion. This means that in only one in.stance did a worm deviate more 

 than 25^ from the normal axis, thus showing a remakably well bal- 



