SECTION OF COVERED-EYED MEDUSZ. 99 
sudden, as if the distant lobe had then for the first 
time received the stimulus. Moreover, one lobe— 
usually one of those adjacent to the lobe directly 
irritated—responds before the other two, and then 
a variable time afterwards the latter also respond. 
This time is, in most cases, comparatively short, the 
usual limits being from a quarter of a second to two 
seconds. How much of these enormous intervals is 
occupied by the period of ganglionic latency, and 
how much by that of transmission, it is impossible 
to say; but I have determined that the rate of 
transmission from the end of a lobe of the manu- 
brium to a lithocyss (deducting a secund for the 
double period of latent stimulation) is the same 
as the rate of a tentacular wave, viz. nine inches a 
second. The presumption, therefore, is that the 
immense lapse of time required for reflex response 
on the part of the manubrium is required by the 
lobular ganglia, or whatever element it is that here 
performs the ganglionic function. 
Exhaustion. 
In various modes of section of Aurelia I have 
several times observed a fact that is worth record- 
ing. It sometimes happens that when the con- 
necting isthmus between two almost severed areas 
of excitable tissue is very narrow, the passage of 
contraction-waves across the isthmus depends upon 
the freshness, or freedom from exhaustion, of the 
tissue which constitutes the isthmus. That is to 
say, on faradizing one of the two tissue-areas which 
