LUMINOUS ORGANS AND LIGHT OF THE PENNATUL^, 251 



hausted, we then find ourselves in the presence of a phenome- 

 non of very great importance and of very splendid appearance. 

 When one manipulates by chance a Pennatula which is in the 

 state we have already called fit for experiment, in every case 

 there is then obtained an appearance of sparks on the polypi- 

 ferous edges, small lights coming and going, as if the light 

 sprung from the finger or from the object which touches the 

 polyp, going always from one to another. If, on the contrary, 

 acting with much rapidity, one applies the stimulant methodi- 

 cally, regular luminous currents will be obtained, as if the little 

 polyps took fire one after another, those on one branch before 

 those of the following one, in such a way that the following 

 conclusion is arrived at : — The fatty matter of the luminous 

 cords may become luminous in the polyps and in the zooids, 

 not only by the excitation acting directly on the polyp and 

 the zooid, but also by stimulants applied to a distant point of 

 the polypidom. In these cases the luminous currents which 

 run along in every direction of the phalanges of polyps and 

 zooids, evidently represent the direction and the velocity of 

 the propagation of the excitation. In the study of the cur- 

 rents observation has been made, in the first place, of their 

 direction ; in the second, of their rapidity. If we operate on 

 the basal extremity of the stalk, we shall have on the stem 

 an ascendant luminous current, if the stimulant is, on 

 the contrary, applied at the top of the polypidom, there will 

 be produced a descendent current. Lastly, if the stimulus 

 is applied to the feathered part of the rachis, one will then 

 obtain two divergent currents. If the two extremities of 

 the polypidom are simultaneously excited, one will have 

 two currents convergent, which usually cease after a period 

 of great vivacity at the point where they meet. I have 

 only once seen in a very sensitive Pennatula the two con- 

 vergent currents continue after thus meeting, each one their 

 own way, as if the other did not exist. If the excitation is 

 produced at the end of a branch, one may see the light run 

 along the stalk, and consequently currents appear on all the 

 other branches in the direction of the diffusion of the excitation. 



Without speaking of the manner employed to measure the 

 velocity of the luminous currents, we shall now give some 

 figures. 



The ascending current of a Pennatula rubra takes to run 

 up the stem, at the minimum \\" , at the maximum S\" , at 

 the average 2^". 



The same current in P. phosphora takes at the minimum 

 li", at the maximum 2^", at the average 2". 



Having observed in all my experiments an interval be- 



