592 WOLFGANG F. EWALD 



tain dyes, especially by eosine. Hertel showed, that Paramaecia 

 and Rotatoria can be killed by light of certain wave-lengths, 

 provided that by artificial staining their protoplasm is put in a 

 position to absorb the light rays acting upon it. Ultra-violet light, 

 however, obtained from the spectrum of magnesium-sparks, 

 had a deadly effect also on unstained animals and was thereby 

 shown to be absorbed by protoplasm under all circumstances. 

 Green light, for instance, would attain the same result only, 

 after eosine was added to the water containing the animals, in 

 a dilution of 1:1200. This effect of certain dyes, because of its 

 similarity to the process of color-sensitisation in photography, 

 has been defined as 'sensitisation' of the protoplasm. Accord- 

 ing to Hertel, it is also possible to make the retractor-muscle 

 of the syphon in Sipunculus directly sensitive to light by staining 

 it with eosine 1 : 3000, while the ventral cord in the same species 

 is stated to be sensitive to light without staining, through natural 

 pigmentation. 



Starting from these experiments I tried to obtain modifi- 

 cations of the light reactions in various marine animals by arti- 

 ficial means. I must confess that my expectation to find changes 

 in the sensibiUty of a given species to colored rays of not 

 excessive intensity by staining the animals, was not fulfilled. 

 Nevertheless, I hope that the results obtained in the other 

 experiments mentioned may justify publication. 



My experiments were carried on in a spacious dark room of 

 the Naples Zoological Institute from February to August 1911. 

 I wish to express my special obligations to the Prussian Minis- 

 try of Education for the use of the table and to Dr. Burian, 

 Dr. Bauer and Dr. Cerutti for their help and advice during the 

 course of my work. 



After some weeks of unsuccessful research the nauplii of Bala- 

 nus perforatus, on which Groom and Loeb had experimented 

 more than twenty years ago, proved to be the most satisfactory 

 objects. These authors have thoroughly investigated and de- 

 scribed the characteristic behavior of the nauphi. After hatch- 

 ing, the larvae show strong positive phototaxis. After being 

 exposed to light for some time they first begin to oscillate between 



