CORRELATION BETWEEN METABOLIC GRADIENTS. 



343 



same lot of tadpoles. No doubt the age of the tadpoles is a factor 

 in the response, as both the electrical gradient and the galvano- 

 tactic response were found by Bellamy to be irregular in older 

 tadpoles. 



TABLE VII. 



ELECTRICAL GRADIENT OF FROG TADPOLES. 



Negative and positive refer to direction of the current through the 

 galvanometer. 



X. SUMMARY. 



1. The idea is advanced that differences of potential in organ- 

 isms, particularly the permanent differences which exist along the 

 main axis of animals, are due to differences in metabolic rate at 

 different regions, the region of highest metabolic rate being the 

 most negative in the external circuit, most positive in the internal 

 circuit. It is further suggested that internal potential differences 

 account for the galvanotactic response, in many animals at least. 

 Data are presented in various groups of animals to show the corre- 

 lation between metabolic differences, electrical differences, and 

 galvanotactic orientation. 



2. In the sponges, Lcucosclcnia and Grantia, the oscular end 

 has usually a higher metabolic rate than, and is electronegative 

 (galv.) to, the basal end. 



3. In the colonial hydroids tested the apical hydranths and levels 



