But the general opinion seems to be that touch in the only sense possessed by the Acalephans, as far es proof luta hitherto gone. That they are sensible to light, though the evidence in favour of their possessing sight properly so called may not be deemed conclusive, will be generally admitted. It is said that some of the smaller tribes have been known to shun a bright light, and to sink into deep water to avoid it.
The chief seat of the touch appears to be in the tentacula and cirrhi with which the majority of Acalephans are furnished. Many of them, as we have ourselves observed, make no sign when wounded extennively in the umbrella or disk.
AboseeMe System:—In roost of the species of Pahneurade Ohs/este distinct muscular fibres exist, which present the peouliax. markings observed on the fibres of voluntary muscles. Where these cannot be seen, tissue consisting of a granular substance exists which possesses the peculiar power of contraction. Professor E. Forbes says, that he has " paralysed one side of a Rhizostoma Aldroandi, whose disk measured more than a foot across, by removing with a scalpel the bands of that half, whilst the other side contracted and expanded as The history of the development of the ova is not less interesting. When first produced they are retained in the interior of the creature until they are covered with cilia, when they pass out, and are found in the water resembling fig. 1. In the course of a little time it attaches itself to some fixed object, and then puts out four arms. In the first stage we have an infusorial animalcule ; in the next, fig. 2, we have a rotifer or hydroid pol3rpe. Not only have we the resemblance to, but some of these forms have been shewn by Steenstrup ('Alternation of Generations') to have been mistaken for permanent states of other animals. The first four arms are succeeded by four more, fig. 3 : at this stage germs or buds frequently grow from its side, fig. 4 : the polypiform body then lengthens, and at last becomes wrinkled, fig. 5 : depressions appear, and the elongated body is cut up into a aeries of usual though with more rapidity, as if the animal were alarmed or suffering." The tentacles of most species are capable of wonderful extension and retraction, movements which must be effected by means of muscular tissue.
Food and Digestion.—The food, small fishes and marine animals, both living and dead, is probably conveyed to the mouth not only by the tentacles and cirrhi with which the greater part of the Medusce are furnished, but also by contractions iu the umbrella or disk itself. Fishes of some size have been found dead and entangled in the tentacles of Medusa., killed most probably by that benumbing or stinging quality which has obtained for them the name of Sea-Nettles. Professor E. Forbes, speaking of the habits of Sarsia tubulosa, says, "being kept in a jar of salt water with small crustacea they devoured these animals, so mach more highly organised than themselves, voraciously, appa rently enjoying the destruction of the unfortunate members of the upper classes with a truly democratic relish. One of them even attacked and commenced the swallowing of a Lizzie octopunetata, quite as good a Medusa as itself. An animal which can pout out its
mouth twice the length of its body, and stretch its stomach to corres ponding dimensions, must indeed be triton among the minnows,' and a very terrific one too." By the investigations of M. Milne-Edwards principally, we now know that all the Pulmograda have gastric cavities, but all have not mouths in the ordinary acceptation of the word. In Rhizostoma, for instance, the only communication between the stomach and the outer surface is carried on through numerous branching canals in the penile arms. In most cases a system of vessels is observed proceeding directly from the stomach, partly nutritive and partly respiratory, but there does not appear to be any diatinct blood-vessels. From the recent researches of Frey, Leuckhart, and E. Forbes, it does not appear that any special blood-fluid exists amongst the species they have examined.
Reproduct ire System and Derelopment.—The majority of the Aealepha3 have very distinct reproductive glands. In the Pulmograda they are placed either on the surface of the sub-umbrella, or on the inner and upper part of the cavity of the peduncle. In most cases these animals appear to be bisexual, though the two sexes are often united in the same individual; but Milne-Edwards, Wagner, and Will have observed individuals with sperm-cells only, and with germ-cells only. Although probably in all cases reproduction takes place by conjunction of these cells, the Med axe, like sonic other lower animals, have the power of producing their offspring by germination. This fact was first made known by Sars in 1836. Professor E. Forbes, in his great work on the British Naked-Eyed 31edusw, says, "I have observed four modes of propagation by germination among the Medusas. 1. Germination from the ovaries, as observed by Sars. 2. Germination from the peduneular stomach. 3. Germination from the walls of a tubular proboscis. 4. Germination from the bases or tubercles of the four marginal tentacles in Sarsia prolifera." In order to suggest the nature of this mode of reproduction, Forbes has the following passage :— " What strange and wondrous changes! Fancy an elephant with a number of little elephants sprouting from his shoulders and thighs, bunches of tusked monsters hanging epaulette-fashion from hia flanks in every stage of advancement. Here a young pachyderm almost amorphous, there one more advanced, but all ears and eyes ; on the right ahoulder a youthful Chirpy, with head, trunk, toes, no legs, and a shapeless body ; on the left, an infant better grown, and struggling to get away, but his tail not sufficiently organised as yet to permit of liberty and free action ! The comparison seems grotesque and absurd, hot it really expresses what we have been describing as actually occur ring among our Naked-Eyed Medusas 1" horizontal slices, from the edges of which tentacles grow, fig. 6 : each layer escapes, and presents itself in the form of a young Medusa, fig. 7. Such is the history given by Steenstrup, in one of the common forms of Pulmograde Medusa, and such with modifications appear to be the changes which each ovum of the Medusa passes through before it becomes a fully developed animal.