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MR. G. J. ROMANES ON THE LOCOMOTOR SYSTEM OE MEDUSAE. 
Medusae, this organ, in the case of Sarsia, is very highly retractile. In fresh and 
lively specimens the appendage in question is carried in its retracted state ; but when 
the animals become less vigorous—from the warmth or impurity of the water in which 
they are confined, or from any other cause—their polypites usually become relaxed. 
The relaxation may show itself in various degrees in different specimens subjected to 
the same conditions ; but in no case is the degree of relaxation so remarkable as that 
which may be caused by removing the periphery of the nectocalyx. For the purpose 
of showing this effect, it does not signify in what condition as to vigour, &c., the 
specimen chosen happens to be in; for whether the polypite prior to the operation be 
contracted or partially relaxed, within half an hour after the operation it is sure 
to become lengthened to a considerable extent. 
In order to show the surprising degree to which this extention may proceed, I 
insert a sketch of a specimen both before and after the operation. The sketches are 
of life size, and drawn to accurate measurement (figs. 9 and 10).* 
Fig’. 9. Fig. 10. 
O o 
With regard to this remarkable effect on the polypite of removing the margin of the 
nectocalyx, it is now to be observed that in it we appear to have very unexceptionable 
evidence of such a relation subsisting between the ganglia of the nectocalyx and the 
muscular fibres of the polypite, as elsewhere gives rise to what is known as muscular 
tonus. This interpretation of the facts cannot, I think, be disputed; and it fully 
explains why, in the unmutilated animal, the degree of elongation on the part of the 
polypite usually exhibits an inverse proportion to the degree of locomotor activity 
displayed by the bell. I may here state that 1 have also observed indications of 
muscular tonus in some of the other Medusae, but for the sake of brevity I shall here 
restrict myself to the consideration of this one case. 
* I may here mention that the fact of the polypite of Sarsia undergoing this extreme elongation after 
the removal of the marginal ganglia, serves to render the artiticial rhythm of the organ under the influence 
of injury, as previously described, all the more conspicuous. 
