PEARSE. — THE REACTIONS OF AMPHIBIANS TO LIGHT. 



195 



average difference between the two thermometers, when placed before 

 the steam pipe was 0.064° C. while that for the light apparatus was 

 0.025° C. The amount of heat received by a thermometer at a distance 

 of thirty centimeters from the heated pipe was therefore more than 

 twice that received when the light apparatus was tested. As the 

 toads were strongly positively phototropic to this light, and as the 

 same individuals were indifferent when placed near the steam pipe, it 

 is safe to conclude that thermo- and photo-reception are distinct 

 processes in the toad's skin, and that, in this animal at least, heat 

 does not give rise to tropic reactions unless there is very strong 

 stimulation. 



Figure 7. Plan of thermometer box. A and B, thermometers; c, c, 

 positions of two of the ten circular openings between the two compartments ; 

 d, slide. 



I. Experiments to determine the Influence of the Central Ner- 

 vous Organs on the Photic Reactions of Amphibians. 



Parker (:05 a ) succeeded in obtaining photic responses from one of the 

 lower fishes (Ammocoetes) after the entire brain had been removed, and 

 he believed that such reactions were brought about by stimulation re- 

 ceived through skin receptors and transmitted through the spinal nerves. 

 To ascertain if similar reactions could be obtained from amphibians, 

 experiments were undertaken with four species. The first to be tested 

 was Rana pipiens. A sharp scalpel was inserted through the dorsal 

 wall of the cranium and a transverse cut was made through the dien- 

 cephalon ; this was followed by another cut behind the second vertebra 

 which separated the cord from the myelencephalon. After such indi- 

 viduals had been tested, they were killed and hardened in alcohol. 

 Subsequent dissection showed that the cuts had been successfully 

 made in ten of the twelve individuals upon which operations had 



