HELIOTKOPISM OF ANIMALS 9 



these pieces would turn toward the light in the same way as 

 the undivided polyps." He cut a number of polyps in two: 

 the anterior halves he placed in one glass, the posterior 

 halves in another. He ound "in oft-repeated experiments 

 that the animals in both glasses collected in the brightest 

 regions in the glass." 



These are, as far as I know, the only extended observa- 

 tions to be found in the old physiological literature of the 

 effects of light upon animals. For a long time no further 

 study of the effects of light upon animals was made. 

 Johannes Muller mentions, in the preface to his Physiologic 

 des Gresichtssinnes, that he made "investigations on the in- 

 fluence of colored light on the vital phenomena of plants and 

 animals," but, as far as I know, the results of his investiga- 

 tions were never published. 



The modern anthropomorphic observations were intro- 

 duced by Paul Bert. Bert raised the question: Do all 

 animals see the same rays that we see? 1 He meant to ask 

 whether all rays of the visible sun spectrum are able to 

 bring about animal movements. An experiment with Daph- 

 nia pulex was sufficient for Bert to settle this question. He 

 projected a spectrum and found that the animals became 

 restless in all positions of the visible spectrum: 



Mes daphnies erraient disperses d'une maniere & peu pres 

 6gale dans toute F^tendue du vase obscur, lorsque soudain je fis 

 tomber sur la fente un rayon colore", un rayon vert. Aussitot elles 

 s'agiterent, se groupment toutes dans la direction de la trainee 

 lumineuse et un tres-grand nombre s'en vint se heurter, montant et 

 descendant sans relache centre la paroi qui recevait la lumiere. 

 Or, un semblable re"sultat fut obtenu pour toutes les regions du 

 spectre visible. Le rouge, le jaune, le bleu, le violet meme atti- 

 raient les daphnies. Seulement il fut facile de remarquer, qu'elles 

 accouraient beaucoup plus rapidement au jaune ou au vert qu'a 

 toute autre couleur. 



!BERT, Archives de physiologic, 1869. 



