700 
MR. Gr. J. ROMANES ON THE LOCOMOTOR SYSTEM OE MEDTJS^E. 
measures about 1^- inch in diameter, and is provided with a polypite of unusual 
proportional size, its length being about f- of an inch and its thickness being also 
considerable. Now if any part of the nectocalyx be irritated, the following series of 
phenomena takes place. Shortly after the application of the stimulus, the large poly- 
pite suddenly contracts, the appearance presented being that of an exceedingly rapid 
crouching movement. The crouching attitude in which this movement terminates con- 
tinues for one or two seconds, after which the organ begins gradually to resume its 
former dimensions. Concurrently with these movements on the part of the polypite, 
the portion of the nectocalyx which was irritated has been gradually bending inwards 
towards the polypite, and by the time that the latter has again become fully extended, 
the portion of the nectocalyx in question has bended inwards as far as it is able. The 
polypite now begins to deflect itself towards the bent-in portion of the nectocalyx ; and 
this deflection continuing with a somewhat rapid motion, the extremity of the polypite 
is eventually brought, with unerring precision, to meet the in-bent portion of the necto- 
calyx. I here introduce a drawing of twice life-size to render a better idea of this 
pointing action by the polypite to a seat of irritation located in the bell (see Plate 30. 
fig. 1). It must further be stated that in the unmutilated animal such action is quite 
invariable, the tapered extremity of the polypite never failing to be placed on the exact 
spot in the nectocalyx where the stimulation is being, or had previously been, applied. 
Moreover, if the experimenter irritates one point of the nectocalyx, with a needle or a 
fine pair of forceps for instance, and "while the polypite is applied to that point he 
irritates another point, then the polypite will leave the first point and move over to the 
second. In this way the polypite may be made to indicate successively any number of 
points of irritation ; and it is interesting to observe that when, after such a series of 
irritations, the animal is left to itself, the polypite will subsequently continue for a 
considerable time to visit first one and then another of the points which have been irri- 
tated. In such cases it usually dwells longest and most frequently on those points 
which have been irritated most severely. 
I think the object of these movements is probably that of stinging the offending body 
by means of the urticating cells with which the extremity of the polypite is armed. 
But, be the object what it may, the fact of these movements occurring is a highly 
important one in connexion with our study of the distribution of nerves in Medusae ; 
and the first point to be made out with regard to these movements is clearly as to 
whether or not they are of a truly reflex character. Accordingly I first tried cutting 
off the margin and then irritating the muscular tissue of the bell ; the movements in 
question were performed exactly as before. These movements, therefore, supply an 
additional instance of the rule laid down in my former paper, viz. : 41 Every Medusa, 
when its centres of spontaneity have been removed, responds to a single stimulation by 
once performing that action which it would have performed in response to that stimu- 
lation had its centres of spontaneity still been intact.” Now the fact of this rule 
holding ' good in this case opens up an interesting subject for our contemplation. It 
