Page:Encyclopædia Britannica, Ninth Edition, v. 1.djvu/145

Rh A C T A C T 129 friend Gains. On the Same day 100,000 sesterces, that could not be invested, were put into the money-box. On the same day a fire broke out in the gardens of Pompey, which arose in the steward s house,&quot; &amp;lt;fec. The Ada differed from the Annals (which were discontinued in B.C. 133) in this respect, among others, that only the greater and more important matters were given in the latter, while in the former things of less note also were recorded. The origin of the Acta is attributed to Julius Caesar, who first ordered the keeping and publishing of the acts of the people by public officers. Some trace them back as far as Servius Tullius, who it was believed ordered that the next of kin, on occa sion of a birth, should register the event in the temple of Venus, and on occasion of a death, should register it in the temple of Libitina. The Acta were drawn up from day to day, and exposed in a public place to be read or copied by all who chose to do so. After remaining there for a reasonable time they were taken down and preserved with other public documents. ACTA SENATUS, among the Romans, were minutes of the discussions and decisions of the senate. These were also called Commentarii Senatus, and, by a Greek name, inrop.vTJfji.aTa. Before the consulship of Julius Caesar, minutes of the proceedings of the senate were written and occasionally published, but unofficially. Caesar first ordered the minutes to be recorded and published autho ritatively. The keeping of them was continued by Augustus, but the publication was forbidden. Some pro minent senator was usually chosen to draw up these Acta. ACT^EON, in Fabulous History, son of Aristaeus and Autonoe, a famous hunter. He was torn to pieces by his own dogs. Various accounts are given of this occurrence; but the best known story is that told by Ovid, who re presents him as accidentally seeing Diana as she was bathing, when she changed him into a stag, and he was pursued and killed by his dogs. ACTIAN GAMES, in Roman Antiquity, solemn games instituted by Augustus, in memory of his victory over Antony at Actium. See ACTIUM. ACTINIA, a genus of ccelenterate animals, of which the sea-anemone is the type. See ACTINOZOA. ACTINISM (from d/ms, a ray), that property of the solar rays whereby they produce chemical effects, as in photography. The actinic force is greatest in the blue and violet rays of the spectrum. ACTINOMETER (measurer of solar rays), a thermo meter with a large bulb, filled with a dark-blue fluid, and enclosed in a box, the sides of which are blackened, and the whole covered with a thick plate of glass. It was the invention of the late Sir John Herschel, and was first described in the Edinburgh Journal of Science for 1825. It is used for measuring the heating power of the sun s rays, the amount of which is ascertained by exposing the bulb for equal intervals of time in sunshine and shade alternately. ACTINOZOA, a group of animals, of which the most familiar examples are the sea-anemones and &quot; coral insects&quot; of the older writers. The term was first employed by de Blainville, to denote a division of the Animal Kingdom having somewhat different limits from that to which its application is restricted in the present article; in which it is applied to one of the two great divisions of the CCELEN- TEKATA, the other being the Hydrozoa. The Actinozoa agree with the Hydrozoa in the primitive and fundamental constitution of the body of two membranes, an ectoderm and an endoderm, between which a middle layer or mesoderm may subsequently arise, in the absence of a completely differentiated alimentary canal, and in possessing thread cells, or nematocysts; but they present a somewhat greater complexity of structure. This is manifest, in the first place, in their visceral tube, or &quot; stomach,&quot; as it is often called, which is continued from the margins of the mouth, for a certain distance, into the interior cavity of the body, but which is always open at its fundus into that cavity. And, secondly, in the position of the reproductive elements, which, in the Hydrozoa, are alwaj^s developed in parts of the body wall which are in immediate relation with the external surface, and generally form outward projections; while, in the Actinozoa, they are as constantly situated in the lateral walls of the chambers into which the body cavity is divided. In consequence of this arrangement, the ova, or sexually generated embryos, of the Actinozoa are detached into the interior of the body, and usually escape from it by the oral aperture; while those of the Hydrozoa are at once set free on the exterior surface of that part of the body in which they are formed. The Actinozoa comprise two groups, which are very different in general appearance and habit, though really similar in fundamental structure. These are 1. The Coralligena or sea-anemones, coral animals, and sea-pens; and 2. The Ctenophora. (1.) The Coralligena. A common sea-anemone presents a subcylindrical body, terminated at each end by a disk. The one of these discoidal ends serves to attach the ordinarily sedentary animal ; the other exhibits in the centre a mouth, which is usually elongated in one direction, and, at each end, presents folds extending down into the gastric cavity. This circumstance greatly diminishes the otherwise generally radial symmetry of the disk, and of the series of flexible conical tentacles which start from it; and, taken together with some other circumstances, raises a doubt whether even these animals are not rather bilater ally, than radially, symmetrical. Each tentacle is hollow, and its base communicates with one of the chambers into which the cavity of the body is divided, by thin membranous lamellae, the so-called mesenteries, which radiate from the oral disk and the lateral walls of the body to the parietes of the visceral tube. The inferior edges of the mesenteries are free, and arcuated in such a manner as to leave a central common chamber, into the circumference of which all the intermesenteric spaces open, while above, it communicates with the visceral tube. The tentacles may be perforated at their extremi ties, and, in some cases, the body wall itself exhibits aper tures leading into the intermesenteric spaces. The free edges of the mesenteries present thickenings, like the hem of a piece of linen, each of which is much longer than the distance between the gastric and the parietal attachment of the mesentery, and hence is much folded on itself. It is full of thread cells. The mesoderm, or middle layer of the body, which lies between the ectoderm and the endoderm, consists of a fibrillated connective tissue, containing fusi form or stellate nucleated cells, and possesses longitudinal and circular muscular fibres. These are prolonged into the mesen teries, and attain a great development in the disk of attach ment, which serves as a sort of foot like that of a limpet. The question whether the Coralligena possess a nervous system and organs of sense, hardly admits of a definite answer at present. It is only in the Actinidce that the existence of such organs has been asserted ; and the nervous circlet of Actinia, described by Spix, has been seen by no later investigator, and may be safely assumed to be non existent. But Professor P. M. Duncan, F.R.S., in a paper &quot; On the Nervous System of Actinia,&quot; recently communi cated to the Royal Society, has affirmed the existence of a nervous apparatus, consisting of fusiform ganglionic cells, united by nerve fibres, which resemble the sympathetic nerve fibrils of the Vertebrata, and form a plexus, which appears to extend throughout the pedal disk, and very probably into other parts of the body. In some of I. 17