But there is another action, namely that of aggregation, which in certain cases may be called reflex, and it is the only known instance in the vegetable kingdom. We should bear in mind that the process does not depend on the previous bending of the tentacles, as we clearly see when leaves are immersed in certain strong solutions. Nor does it depend on increased secretion from the glands, and this is shown by several facts, more especially by the papillae, which do not secrete, yet undergoing aggregation, if given carbonate of ammonia or an infusion of raw meat. When a gland is directly stimulated in any way, as by the pressure of a minute particle of glass, the protoplasm within the cells of the gland first becomes aggregated, then that in the cells immediately beneath the gland, and so lower and lower down the tentacles to their bases;— [page 243] that is, if the stimulus has been sufficient and not injurious. Now, when the glands of the disc are excited, the exterior tentacles are affected in exactly the same manner: the aggregation always commences in their glands, though these have not been directly excited, but have only received some influence from the disc, as shown by their increased acid secretion. The protoplasm within the cells immediately beneath the glands are next affected, and so downwards from cell to cell to the bases of the tentacles. This process apparently deserves to be called a reflex action, in the same manner as when a sensory nerve is irritated, and carries an impression to a ganglion which sends back some influence to a muscle or gland, causing movement or increased secretion; but the action in the two cases is probably of a widely different nature. After the protoplasm in a tentacle has been aggregated, its redissolution always begins in the lower part, and slowly travels up the pedicel to the gland, so that the protoplasm last aggregated is first redissolved. This probably depends merely on the protoplasm being less and less aggregated, lower and lower down in the tentacles, as can be seen plainly when the excitement has been slight. As soon, therefore, as the aggregating action altogether ceases, redissolution naturally commences in the less strongly aggregated matter in the lowest part of the tentacle, and is there first completed.