ME. a. J. ROMANES ON THE LOCOMOTOR SYSTEM OF MEDUSAE. 
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interdigitating cuts in the strip itself, which system it is unnecessary again to describe. 
Blocking may also be caused by pressure exerted at any line which crosses the con- 
tractile strip transversely. In such cases the time during which the pressure lasts, 
and the intensity of the pressure while it does last, are the principal factors in 
determining the blockage of contractile waves, as well as the time during which such 
blockage will continue after the pressure has been removed. Y arious poisons also cause 
blocking of contractile waves, the obstruction to the passage of the waves being always 
very precisely restricted to the line in the strip where the poisoned water ends, or, it 
injections be used, where the injected poison is present. If a long portion of a con- 
tractile strip be immersed in the solution of a poison which will eventually cause a 
blocking of the waves, it is observable that for some little time before the blocking- 
takes place the rate of transmission of the waves becomes progressively slowed. 
The presence of a visual sense has been demonstrated in the case of the genus Sarsia, 
and its seat localized in the so-called eye-specks. It has also been proved that in this 
the first appearance of a visual organ in the animal series the rays by which the organ 
is affected are the properly luminous rays, and not the thermal rays beyond the luminous 
spectrum, as has been reasonably inferred from the position of the pigment-spot in 
relation to the other parts of the visual structure. 
With regard to poisons, I confine myself on this occasion to briefly detailing the 
effects of only a few; and these effects are chosen for description in order to indicate 
the apparent functional identity of the locomotor centres of Medusae, and of the 
relations which these centres bear to the contractile tissue of the swimming-organs, with 
the nervous tissue of all higher animals, and the relations which this bears to muscular 
tissue. Chloroform, ether, alcohol, morphia, strychnia, and curare all assert their 
several peculiar influences on the locomotor movements of the Medusae, and this in 
all the particulars and with all the distinctness which is characteristic of their action 
on nervous tissues in general. 
Received March 24, 1876. 
Postscript III. 
On the 3rd of February, 1876, I received the following communication from Dr. 
Lutken, of Copenhagen : — 
“ With reference to your interesting note in ‘Nature,’ November 12th, 1874, your 
attention is drawn to Dr. Elmer’s paper on the artificial divisibility &c. in Aurelia 
aurita and Cyancea cajyillata, Wurzburg ‘ Verhandlungen,’ vi. (1874).” 
The note here referred to is one which I sent to ‘ Nature ’ in September 1874, and 
which was published in November of that year. In this note I described the effects, on 
a species of naked-eyed Medusa, of what in this memoir I call the fundamental experi- 
