86 J. M. D. OLMSTED 



Since Planaria maculata has no otocyst, it may be that after 

 eating, the food in the digestive tract serves as an otolith, and 

 after digestion and assimilation the animal becomes indifferent 

 to gravity because the food is no longer able to press upon the 

 digestive epithelium. This does not account for the fact that 

 fed worms are positively geotropic when first put in the dark. 



I wish to thank Dr. Parker for suggesting the problem and 

 for advice as to methods. 



CONCLUSIONS 



1. Unfed Planaria maculata which have been in the light are 

 positively geotropic when first placed in the dark. After several 

 days in the dark they become indifferent to gravity. 



2. Fed Planaria maculata which have been kept in the light 

 are likewise positively geotropic at first. But they become nega- 

 tive after two days and indifferent after five days. 



3. Fed planarians which have been in the dark for some time 

 are negatively geotropic. 



4. The presence or absence of slime tracks has no influence 

 on the geotropism of these planarians. 



REFERENCES 



Bardeen, C. R. On the Physiology of the Planaria maculata with Especial Refer- 



1901. ence to the Phenomena of Regeneration. Amer. Jour. Physiol., 

 vol. 5, pp. 1-55. 



Kafka, G. Einfiihrung in die Tierpsychologie auf experimenteller und etholo- 



1914. gischer Grundlage. Leipzig, 8vo., xii+593 pp. 

 Pearl, R. The Movements and Reactions of Fresh-water Planarians: A Study 



1902. of Animal Behavior. Quart. Jour. Micr. Sci., vol. 46, pp. 508-714. 

 Walter, H. E. The Reactions of Planarians to Light. Jour. Exp. Zool., vol. 5, 



1908. pp. 35-162. 

 Whitehouse, R. H. The Natural History of Planarians. Irish Naturalist, vol. 

 1914. 23, pp. 41-47. 



