332 



PHYSIOLOGY OF THE INVERTEBRATA. 



exciting the nerve at a point near the muscle, and notin 

 moment of excitation and the moment of contraction, ( 

 able to ascertain the time which, elapses between th( 

 phenomena : the same experiment is then repeated on a 

 of the nerve further from the muscle. The difference i 

 time observed in these two experiments — that is to sa; 



P 



Fig. 66. — Apparatus foe Studying the Transmission of Moti 

 Excitation in the Nerve of the Chela. 



M = myograph carrying claw of Homarus. s = style attached to the 

 opodite. r = elastic spring which holds the dactylopodite. a = 



electrodes, b = another pair of electrodes. C = commutator. P = 1 

 E = registration cylinder. BB' = the two coils. A = steel needles for 

 the circuit at each revolution of the cylinder. 



lapse of time between the second contraction and the f 



gives the time employed by the motor excitation to rn 



distance between the two excited points. Knowing 



distance, one can calculate the rate of transmission. 



Predericq and Vandevelde exposed the nerve (in a ' 



lobster) which leads to the claw by two openings. A i 



* The style used was that of Dr. Marey, the distinguished Profei 

 Experimental Physiology in the College of France. 



