ME. GL J. EOMANES ON THE LOCOMOTOE SYSTEM OE MEDUSAE. 
311 
number and strength of the previous contractions. This is no doubt true as a general 
statement, and as such is what might have been anticipated ; but I do not think that a 
number of observations would tend to establish any more precise relation. In the case 
of Sarsia the alternations between periods of rapid swimming and periods of complete 
repose are much more marked than in Aurelia aurita , to which Dr. Eimer’s tables refer ; 
and I am sure that with them the rule in question can only apply in a very general 
way. It is to be observed that Dr. Eimer himself does not appear to place much 
reliance on particular applications of this rule. 
I am able to confirm Dr. Eimer’s statements as to the various ways in which the 
lithocysts discharge their influence relatively to one another, and would only add the 
curious fact that very frequently one or more of the eight lithocysts appears to be tem- 
porarily or permanently prepotent over the others — the contractions always originating 
in it for a great number of times in succession. 
Mere observation with the eye, however, is not sufficient to determine the interesting 
question as to whether or not there is any further coordination between the lithocysts 
than is brought about by the rapid passage of contractile waves from one to the other. 
I have accordingly made a large number of variously devised sections with the view 
of answering this question ; but it would occupy too much space to detail them at 
present. I may state, however, that Dr. Eimer is quite right in his assertion that 
in no case can a contraction of one zone take place without being accompanied by a 
synchronous, or almost synchronous, contraction of all the others ; and not only so, but 
in all my forms of section I find it to be universally true, that as soon as a contrac- 
tile wave which starts from one lithocyst arrives at another (no matter how far off or 
how feeble the residuum of the contractile wave may be), the latter is immediately 
stimulated into activity, liberates a powerful discharge, and so originates a new wave of 
contraction. Thus, for instance, it is not difficult to obtain a series of lithocysts con- 
nected in such a manner that the resistance offered to the passage of the waves by a 
certain width of the junction tissue is such as just to allow the residuum of the con- 
tractile wave which emanates from one lithocyst to reach the adjacent lithocyst, thus 
causing it to originate another wave, which in turn is just able to pass to the next litho- 
cyst in the series, and so on, each lithocyst in turn acting like a reinforcing battery 
to the passage of the contractile wave. But, as already observed, it does not fall within 
the scope of the present paper to discuss the subject of coordination among the loco- 
motor centres of Medusae. I may state, however, that there appears to be important 
differences between the discophorous naked-eyed Medusae and the true Discophora in 
this respect ; for in all the species of the former which I have as yet observed, the area 
of paralysis in the nectocalyx corresponds much more precisely with the line of ganglionic 
tissue which has been removed from its margin than it does in the case of the true 
Discophora. 
I cannot quite assent to the description which Dr. Eimer gives of the contractions 
which sometimes supervene in the umbrella of Aurelia aurita when all the lithocysts have 
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