HELIOTROPISM 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 found “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 Miller mentions, in the preface to his Physiologie 
des Gesichtssinnes, 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?’ 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 dispersées d’une maniére & peu prés 
égale dans toute |’étendue du vase obscur, lorsque soudain je fis 
tomber sur la fente un rayon coloré, un rayon vert. Aussitét elles 
s’agitérent, se groupérent toutes dans la direction de la trainée 
lumineuse et un trés-grand nombre s’en vint se heurter, montant et 
descendant sans relache contre la paroi qui recevait la lumiére. 
Or, un semblable résultat fut obtenu pour toutes les régions du 
spectre visible. Le rouge, le jaune, le bleu, le violet méme 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. 
1BeERT, Archives de physiologie, 1869. 
Digitized by Microsoft® 
