ME. GL J. EOMAjSTES ON THE LOCOMOTOE SYSTEM OE MEDUSA. 
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along each side, and the contractile waves passing without impediment from end to end. 
But what I wish more especially to observe just now is, that by progressively increasing 
the number of such interdigitating cuts up to the point at which the contractile wave 
is blocked and then leaving the tissue to recover itself, in many cases it will be observed 
that the blocking is sooner or later overcome, that on then adding more interdigitating 
cuts the blocking again supervenes, but that in time it may again be overcome, and so 
on. It is, however, comparatively rare to find cases in which blocking is overcome 
twice or thrice in succession. 
(i e ) Section is not the only way in which blocking of waves may be caused in contrac- 
tile strips. I find that pressure, even though very gentle, exerted on any part of a 
strip causes a blocking of the waves at that part, even after the pressure has been 
removed. If the pressure has been long continued, after its removal the blocking will 
probably be permanent ; but if the pressure has been only of short duration, the blocking 
will most likely be transitory. Even the slight strains caused by handling a contractile 
strip in the air are generally followed by a decrease in the rate of the waves, and some- 
times by their being completely blocked. Other methods by which the passage of 
waves in contractile strips admits of being blocked will be alluded to further on. 
{f) Such are some of the facts I have been able to collect bearing on the question 
concerning the physiological character of the general contractile tissues of the Medusse. 
That these facts are of a somewhat paradoxical nature is evident ; and whether or not 
there is any theory by which they admit of being satisfactorily reconciled is doubtful. 
I may say, however, that I think there is such a theory, and that I only refrain from 
publishing it at the present time because I think that at this early stage of the inquiry 
it is desirable, as much as possible, to avoid speculation. 
Y. Additional pacts tending to prove the identity op the specialized marginal 
tissue op Medusa: with nervous tissue in general. 
§ 1. Sense-organs . — It has long been thought more or less probable that the so-called 
“eye-specks” of Medusae are rudimentary or incipient organs of vision; but I am not 
aware that any one has hitherto endeavoured to test the supposed probability by experi- 
ment. I say “ supposed probability,” because, in the absence of any structural resem- 
blance to an ocellus, I do not see how speculation as to the function of these organs can 
be of any further value than a guess*. The guess, however, in this case happens to be 
correct. 
* [Postscript II. — It is -with considerable pleasure that I am now able to add the following very judicious and 
philosophical confirmation of this opinion by so high an authority as Prof. Haeckel : — “ Die Deutung der Sinnes- 
organe niederer Thiere gehort ohne Zweifelzuden schwierigsten Objecten dervergleichendenPhysiologie und ist 
der grossten Unsicherheit unterworfen. Wir sind gewohnt, die yon den Wirbelthieren gewonnenen Anschauungen 
ohne Weiteres auch auf die wirbellosen Thiere der yerschiedenen Kreise zu iibertragen und bei diesen analoge 
Sinnesempfindungen anznnehmen, als wir selbst besitzen.” Prof. Haeckel, indeed, inclines to the belief that 
the marginal vesicles which he examined are sense-organs of some kind ; but this is a very different position 
2 T 2 
