190 



Dr. A. D. Waller. On the 



[July 17, 



In the early stages — when presumably the blastodermic membrane 

 has not yet become folded to form a tubular embryo — the blaze- 

 currents aroused by both directions of excitation are positive or 

 ascending. 



At a more advanced stage of development the blaze-currents are 

 usually homoclrome with the direction of excitation, viz., positive or 

 ascending after a positive or ascending excitation, and negative or 

 descending after a negative or descending excitation. 



In some cases, but with such infrequency as to deserve to be charac- 

 terised as exceptional, both responses have been observed to occur in 

 a negative or descending direction. This may have been due to 

 attachment of the embryo to the shell. 



[I have made a few observations on frog's spawn, and although these 

 have not yet been sufficient to enable me to specify the conditions of 

 the presence or absence of the reaction, I think that the fact of its 

 presence is worth reporting, as well as the further fact that in some 

 cases of undoubtedly living spawn I have failed to detect it.] 



+•02 



-00 



•01 



-02 















1 











^073. 



5 10 m ins. 



Frog's Spawn. — Two homoclrome responses of + and — 0*022 volt to excitation 

 by break current at + and — 5000. 



10 20 30 mins. 



Frog's Spawn. — Series of homodrome responses to series of single break induction 

 currents 5000 + at intervals of two minutes. 



