My own experience incontestibly proves that the suckers in question are used for precisely the same purpose as those situated in any other part of the body. I am enabled to state, from having repeatedly witnessed the phenomenon, that _the Echinus can walk about with equal facility while lying on its back as in its more natural position_. The advantage of this power to the animal under certain circumstances will be apparent upon a little reflection. With regard to the spines, I fancy their purpose is almost solely to assist the Urchin to burrow in the sand, and to protect it from the attacks of its enemies. It may be, however, that at particular times they serve as aids to locomotion, but that their assistance can be, and is, often dispensed with entirely by the animal, I can most positively assert. My experiments were always conducted in glass vases, up the smooth, polished sides of which my specimens frequently advanced. Upon reaching the surface of the water, I have seen an Urchin roll completely round and move along on its back, then after a time change its position, and travel round the circumference of the vessel _while attached by its side_, the body of the animal being sometimes inverted. At such times as these it must be quite evident that the spines would be totally useless, and that by the suckers alone did the animal perform its interesting movements. According to a certain writer, there are some foreign species of the Echini remarkable for possessing spines, which act both as offensive and defensive weapons. 'On one occasion' (this writer says) 'when searching for a fish in the crevice of a coral rock, I felt a severe pain in my hand, and upon withdrawing it, found my fingers covered with slender spines, evidently those of the Echinus, of a grey colour, elegantly banded with black. 'They projected from my fingers like well-planted arrows from a target, and their points being barbed could not be removed, but remained for some weeks imbedded as black specks in the skin. Its concealed situation did not permit me to examine this particular Echinus. In some experiments I approached the spines with so much caution, that had they been the most finely pointed needles in a fixed state no injury could have been received from them, yet their points were always stuck into my hand rapidly and severely.' In addition to those above described, the Sea-Urchin is provided with other organs, in shape somewhat resembling minute pincers, supported on fleshy stems, which always keep up an incessant motion when the animal is in a healthy condition. They are scattered in great numbers over the surface of the body, among the spines, and around the mouth of the Urchin.