842 
MR. a. J. ROMANES AND PROFESSOR J. C. EWART 
however, even more energetic in executing their righting movements—raising their 
discs high above the tank floor upon their long arms, and completing their movements 
in a few seconds. So vigorous are these Star-fish, that they are able to execute this 
manoeuvre even upon a dry table, although the weight to be overcome is so much 
greater in air than in water. 
It may be added that these Star-fish are not able to ascend perpendicular surfaces, 
owing to the rudimentary condition of their ambulacra! apparatus. 
2. Echini. —In striking contrast to the rapid locomotion of the Echinoderms last 
considered, stands the slow locomotion of the Echinus, which along a horizontal surface 
takes place at the rate of only 6 inches per minute, and up a perpendicular surface at 
the rate of 1 inch in 4 minutes. Looking to the slowness of this rate of locomotion, it 
must strike us as a curious fact that there is, perhaps, no animal which can properly 
be said to approach the Echinus in respect of the number and elaboration of special 
mechanisms subservient to the function of locomotion. Careful observation has 
satisfied us that these special mechanisms are four in number, and each of these 
displays an immense amount of elaboration. We may best consider these four 
mechanisms by taking them separately. 
(A.) Ambulacral feet, or pedicels. —This system is both structurally and functionally 
closely similar to the homologous and analogous system in Star-fishes. In the Echinus, 
however, it is of more use than in the Star-fish as a system of anchors and feelers. 
The form of the Echinus being globular, while that of the Star-fish is flat, it follows 
that the animal is more exposed to the displacing influence of currents, because offering 
a larger surface for their action. Consequently, a need arises for a more secure system 
of attaching the animal to the surfaces over which it may be crawling, and this need 
is supplied by the ambulacra! feet acting more the part of anchors than they do 
in the Star-fish. Thus it is that in forcibly removing an Echinus from whatever 
surface it may be adhering to, a much greater resistance is encountered than one finds 
in the case of Star-fish, and—especially if a little time is given to the animal after 
a first alarm to establish a firmer hold—the suckers stick so tightly that a certain 
number allow themselves to be torn from the organism rather than leave go their 
attachments—these suckers being therefore left behind, fastened upon the surface to 
which they were adhering. Under similar circumstances a Star-fish will never thus 
leave its suckers behind. Indeed, a Star-fisli does not seem to fear abandoning itself 
to the mercy of currents ; for, as we shall subsequently see, a very small amount of 
provocation will induce it to abandon its hold of a perpendicular surface spontaneously, 
in order to effect its escape by falling through the water. An Echinus, on the other 
hand, always seems, as it were, nervously anxious about its anchorage—in all its 
movements its first concern appearing to be to have its steadiness amply secured by a 
sufficient number of suckers, and this even in the perfectly still water of a tank. 
The other function of the pedicels which is peculiar to the Echinus, viz., that of 
feelers, also no doubt arises from the shape of the animal; for while in the Star-fish 
