846 
MR, G. J. ROMANES AND PROFESSOR J. C. EWART 
lantern having been, as it were, left behind by the movement of the shell over it as a 
pivot, and therefore sloping away from the direction of advance at the same angle as 
that with which it had previously sloped towards it. The lantern is now again 
retracted, and during its retraction, partly rotated upon its horizontal axis, so that by 
the time it is again protruded, its vertical axis is again pointing towards the direction 
of advance. And so the manoeuvre is repeated over and over again—the Echinus 
advancing by a succession of jerks as it repeatedly tumbles over its teeth. As already 
stated, the movements of the lantern are rythmical, and therefore the jerks take place 
at regular intervals. It is important, however, to observe that although the lantern 
is thus used to assist the spines in locomotion, it is doubtful whether such is the full 
explanation of the lantern’s movements. For, on the one hand, it is certain that 
these movements are not necessary, but only accessory to locomotion ; and, on the 
other hand, they continue to take place under circumstances where they can be of no 
use in locomotion. Thus we have observed that young specimens of Echinus do not 
use their lanterns for locomotion, as older specimens always do. Probably the older, 
and therefore larger specimens, use their lanterns more than the younger and smaller 
ones, on account of having to move so much heavier a mass. Also, the relatively 
greater length of the spines in the smaller specimens makes it much more difficult 
for the lantern to touch the table. This view is confirmed by the fact that, on cutting 
the spines of young specimens shorter, these small Echini begin to use their lanterns 
after the manner of larger specimens. But, be this as it may, the fact that in young- 
specimens the lanterns rarely touch the table is proof that the spines are here alone 
sufficient to produce locomotion. Again, as before observed, these peculiar movements 
of the lantern take place under circumstances where they can be of no use in pro¬ 
ducing locomotion. Thus, for instance, they take place in young specimens in the 
same way as in old, although, as just stated, the lanterns in this case do not touch the 
table at all. And again, if an Echinus be placed on its aboral pole, the lantern at 
once begins its rhythmical movements, and continues them as long as the animal 
remains in that position. In this case there is added to the movements already 
described another perfectly rhythmical movement, which consists in closing and 
opening the teeth—the time of complete closure corresponding with that of greatest 
profusion, and the time of fullest opening with that of greatest retraction. It appears, 
therefore, that these rhythmical movements of the lantern, although undoubtedly of 
use in assisting locomotion in some cases, may possibly have some other function to 
perform in the economy of the animal. Whether this is so or not, there seems to be 
some intimate connexion between these movements of the lantern and the move¬ 
ments of the spines ; for when one stops the other stops, and when one begins the 
other begins. The movements of the lantern may best be studied by taking away 
the top of the Echinus shell, and looking down upon the lantern from above; it may 
then be seen exhibiting its rhythmical movements, which when thus viewed forcibly 
remind one of the rolling of a ship at sea. The complex muscular system of the 
