710 
ME. G. J. ROMANES ON THE LOCOMOTOR SYSTEM OF MEDTJS2E. 
ness, in the latter it is exceedingly prolonged and gradual, occupying some four or five 
seconds in its execution, and, from its slow but continuous nature, presenting a graceful 
appearance. Lastly, the difference between the two kinds of contraction is shown by 
the fact that, while a spasm is gradually passing off, the ordinary rhythmical contrac- 
tions may often be seen to be superimposed on it — both kinds of contraction being thus 
present in the same tissue at the same time. 
(b) I have thus given a somewhat fuller description of these movements than that 
contained in my former paper, because, as the whole of the present section is to be occu- 
pied with their consideration, it seems desirable to render a complete account of them 
at the outset. Now the point with which we shall be especially concerned on the pre- 
sent occasion is one which has already been alluded to incidentally, viz. that in the case 
of Staurophora laciniatct it is only stimulation of certain parts of the organism which 
has the effect of throwing it into a spasm. These parts are the margin (including the 
tentacles) and the courses of the four radial tubes (including the polypite, which in this 
species is spread over the radial tubes). This limitation, however, is not invariable ; for 
I have often seen individuals of this species respond with a spasm to irritation of the 
general contractile tissue. Nevertheless, such response to such stimulation in the case 
of this species is exceptional — the usual response to muscular irritation being an ordinary 
locomotor contraction, which forms a marked contrast to the tonic spasm that invariably 
ensues upon stimulation of the margin, and almost invariably upon the stimulation of a 
radial tube. Still it must here be carefully noted, that in at least three other species 
belonging to another genus, viz. Tiaropsis diademata , T. polydiademata, and T. oligo- 
plocama, spasmodic movements in no way distinguishable from those of Staurophora 
laciniata invariably follow upon stimulation of any part of the organism , or even of a 
minute portion of the contractile tissue when excised. Hence the usual failure of 
Staurophora laciniata to respond spasmodically to irritation of its contractile tissues is 
probably due to their being somewhat less irritable than those of the other species 
named. 
(c) For my investigation of these spasmodic movements I chose Staurophora laciniata 
because, from its large size, it admitted of my performing various modes of section which 
would be impracticable in the case of the other naked-eyed Medusse. Moreover, as the 
principal point to be inquired into had reference to the fact that these movements were 
most readily elicited by stimulating the marginal or radial tubes, this species seemed 
particularly well suited to the purposes of my inquiry; for, as we have just seen, the 
degree of its irritability is such as to cause the animal to respond spasmodically to the 
slightest irritation of the marginal or radial tubes, while even to violent irritation of the 
contractile tissues the only response is a locomotor contraction. The first point I endea- 
voured to settle was whether the faculty of originating a tonic spasm in answer to a 
stimulus was absolutely restricted, in the case of Staurophora laciniata , to the marginal 
and radial tubes, or such faculty was likewise shared by a small band of the contractile 
tissue in the immediate neighbourhood of these tracts. 
