_Special Senses._ Before concluding, I must say a few words on the experiments whereby we sought to test for the presence in Echinoderms of the special senses of sight and smell. We have found unequivocal evidence of the Star-fish (with the exception of the Brittle-stars) and the Echini manifesting a strong disposition to crawl towards, and remain in, the light. Thus, if a large tank be completely darkened, except at one end where a narrow slit of light is admitted, and if a number of Star-fish and Echini be scattered over the floor of the tank, in a few hours the whole number, with the exception of perhaps a few per cent., will be found congregated in the narrow slit of light. The source we used was diffused daylight, which was admitted through two sheets of glass, so that the thermal rays might be considered practically excluded. The _intensity_ of the light which the Echinoderms are able to perceive may be very feeble indeed; for in our first experiments we boarded up the face of the tank with ordinary pinewood, in order to exclude the light over all parts of the tank except at one narrow slit between two of the boards. On taking down the boards we found, indeed, the majority of the specimens in or near the slit of light; but we also found a number of other specimens gathering all the way along the glass face of the tank that was immediately behind the pine-boards. On repeating the experiment with blackened boards, this was never found to be the case; so there can be no doubt that in the first experiments the animals were attracted by the faint glimmer of the white boards, as illuminated by the very small amount of light scattered from the narrow slit through a tank, all the other sides of which were black slate. Indeed, towards the end of the tank, where some of the specimens were found, so feeble must have been the intensity of this glimmer, that we doubt whether even human eyes could have discerned it very distinctly. Owing to the prisms at our command not having sufficient dispersive power for the experiments, and not wishing to rely on the uncertain method of employing coloured glass, we were unable to ascertain how the Echinoderms might be affected by different rays. On removing with a pointed scalpel the eye-spots from a number of Star-fish and Echini, without otherwise injuring the animals, the latter no longer crawled towards the light, even though this were admitted to the tank in abundance; but they crawled promiscuously in all directions. On the other hand, if only one out of the five eye-spots were left intact, the animals crawled towards the light as before. It may be added that single detached rays of Star-fish and fifth-part segments of Echini crawl towards the light in the same manner as entire animals, provided, of course, that the eye-spot is not injured.