342 L- H. HYMAN AND A. W. BELLAMY. 



There is thus in oligochaetes a remarkable correspondence be- 

 tween the double gradient, the electrical gradient, and galvano- 

 taxis. The U-attitude assumed in the current is consistent with 

 the double respiratory gradient and double electrical gradient 

 found in these forms. Particularly striking is the cathodic ori- 

 entation of those forms of which the anterior end is positively 

 charged (int.) and the anodic orientation of those of which the 

 anterior end is negatively charged (int.). 



IX. TADPOLES. 



Although some fragmentary data have been obtained on other 

 vertebrate young, we shall confine our discussion for the present 

 to frog tadpoles. 



1. The Metabolic Gradient. This has not been determined for 

 tadpoles, but from the condition in earlier stages of the frog 

 (Bellamy, '19) and in other vertebrate embryos it is probable that 

 the posterior end has the highest metabolic rate of any part. 



2. The Electrical Gradient. Hyde ('04) tested the potential 

 differences along the axis of toad ( ?) tadpoles and states that 

 there is a permanent difference along the axis " in a direction from 

 the tail to the head of the embryo." The meaning of this is not 

 very clear, but from the usage throughout the paper it appears that 

 Hyde means that the tail is negative (galv.) to the head. This 

 was also found to be the case by Bellamy in frog tadpoles. The 

 data are given in Table VII. In nearly all cases the head was 



o j 



found to be positive (galv.) to body and tail. 



3. Galvanotaxis. It has been known since 1885, when Hermann 

 discovered the fact, that frog tadpoles are anodic i.e., when placed 

 in a current, they turn their anterior ends toward the anode, tails 

 to the cathode, bodies in line with the current. This statement we 

 have verified. This orientation in the current corresponds com- 

 pletely with the electrical differences of potential found in the 



8 In a previous paper (Hyman, '18) it was erroneously stated that Miss 

 Hyde had determined that the anterior end of vertebrate embryos is negative 

 to the posterior end. She found a permanent difference of potential along 

 one axis of the blastoderm but was unable to determine the direction of 

 the current with reference to the future embryo, owing to the young stages 

 with which she worked, except in the case of the tadpoles, where her mean- 

 ing is not clear. 



