38 COMPARATIVE PHYSIOLOGY OF THE BRAIN 



aquarium (equally near the surface), a Ciona freshly 

 operated upon and a normal Ciona. The minimum 

 height from which a contraction could be produced 

 was as follows for the normal animal (a) and the 

 animal operated upon (<) : 



a (normal) b (operated) 



8 mm 65 mm 



4 mm 75 mui 



10 ;;/;;/ 80 mm 



80 mm 



In two other animals used for the experiment I 

 obtained the following values : 



a (normal) b (operated) 



6 mm 22 mm 



8 mm 20 mm 



It seems to me that the difference in the irritability 

 arises from the fact that in the normal Ascidian the 

 stimulation is conducted through the nerves and the 



o 



ganglion, in which case less energy is required. In 

 the Ascidian operated upon, however, the muscles are 

 stimulated directly, and the conduction of the stim- 

 ulation probably takes place from muscle-cell to 

 muscle-cell, just as in the heart. We know, more- 

 over, that the direct irritability of muscle-fibres is not 

 so great as that of the nerves. Hence the nerves and 

 the ganglion only play the part of a more sensitive and 

 quicker conductor for the stimulus (i). 



2. It may seem as though no conclusions could 

 be drawn from these cases in regard to the " reflex 



