844 
MR, G. J. ROMANES AND PROFESSOR J. C. EWART 
into this position by means of the slender motive power available can be at once 
appreciated on witnessing the performance, so that one is surprised, notwithstanding 
the co-ordination displayed by all the suckers, that they are able to accomplish the 
work assigned to them. That the process is in truth a very laborious one is manifest, 
not only from the extreme slowness with which it takes place, but also because in the 
case of not perfectly strong specimens complete failure may attend the efforts to reach 
the position of resting on the equator—the Echinus after rearing up a certain height, 
becoming exhausted and again falling back upon its ab-oral pole. Moreover in some 
cases it is interesting to observe that when the equator position has been reached with 
difficulty, the Echinus, as it were, gives itself a breathing-space before beginning the 
movement of descent—-drawing in all its pedicels save those which hold it securely in 
the position to which it has attained, and remaining in a state of absolute quiescence 
for a prolonged time. It then suddenly begins to protrude all its feet again, and to 
continue its manoeuvre. At any time during such a period of rest, a stimulus of any 
kind will immediately determine a re-commencement of the manoeuvre. 
It will be perceived that as soon as the position just described has been attained, 
gravity, which had hitherto been acting in opposition to the righting movement, now 
begins to favour that movement. It might, therefore, be anticipated that the Echinus 
would now simply let go all its attachments, and allow itself to roll over into its natural 
position. But an Echinus will never let go its attachments without some urgent 
reason ; and in this case it lets itself down almost as slowly as it raised itself up. So 
gently, indeed, is the downward movement effected, that an observer can scarcely tell 
the precise moment at which the righting is concluded. Therefore, in the downward 
movement, the feet, which at the earlier part of the manoeuvre were employed 
successively in rearing the globe upon its equator, are now employed successively in 
preventing its too rapid descent (Plate 83, fig. 26). 
Several interesting questions arise with reference to these righting movements of 
Echinus. First of all we are inclined to ask what it is that determines the choice of 
the rows of feet which are delegated to effect the movements. As the animal has a 
geometrical form of perfect symmetry, we might suppose that when it is placed upon 
its pole, all the five rows of feet would act in antagonism to one another; for there 
seems nothing more to determine either the action or the inaction of one row rather 
than another. The answer to this question is not very clear. First of all it occurred 
to us that, although the form of the animal presents a geometrical symmetry, the 
anatomy of the animal is not symmetrical, and therefore that some of the feet-rows 
might be functionally prepotent over the others. But on observing a great number of 
specimens, we satisfied ourselves that among different individuals any homologous 
rows of feet might be used indiscriminately— i.e., taking the madreporic plate as the 
point of reference, we found that in different individuals rotation might take place in 
any direction with reference to that plate indifferently. On the other hand, individual 
specimens would sometimes manifest a marked tendency to rotate in one direction, 
