JOURNAL OF ANIMAL BEHAVIOR 



Vol. 7 JANUARY-FEBRUARY No. 1 



NEW EXPERIMENTS ON THE LIGHT REACTIONS 

 OF PLANTS AND ANIMALS' 



CARL VON HESS 



I 



Gentlemen: Allow me, before the order of the day, to give 

 a brief report of a discovery, which, though it stands only in 

 loose relation to our theme, seems to me of general interest. I 

 speak of the accommodation of the alciopids. 



The alciopid is, as you know, a nearly transparent pelagic 

 annelid, whose comparatively highly developed eyes have been 

 repeatedly the object of histological research. It was believed 

 that muscular elements could be demonstrated anatomically in 

 these eyes and on this supposition theories of the act of accom- 

 modation were grounded. These theories can easily be proved 

 mistaken, as the following shows; I will not further dwell on them. 



On account of the small size of the eyes the largest — which 

 I was enabled to examine had a diameter of hardly 1 mm., — it 

 had been considered heretofore impossible to attack the prob- 

 lem of their accommodative changes experimentally. 



However, I was able, by laying the living and carefully iso- 

 lated eyes on suitable electrodes, under seawater, and by ob- 

 serving them through binocular lenses in a very strong light 

 falling from above, to follow the changes caused by electric 

 irritation, and thus to discover a most remarkable accommo- 

 dative process, unique in the animal world. 



At another time I shall describe this process in detail, tonight 



I shall limit my description to the main facts. 



1 A lecture before the Morphological Society of Munich, reported and trans- 

 lated by Miss Hilda Lodeman. 



