CIRCULATORY SYSTEM. 763 CIRCUMCISION. the respiratory functions of the circulutory sys- tem are largely replaced by respiratory lubes which ramify even to the muscles. There is al- ways a lieart, however, and in Aruchuoidea a number of welldetined blood-vessels. In citcbralcs the organs of circulation are the heart, arteries, veins, and lymphatics. The heart is the central organ of the circul.TCOry system. To it the blood is drawn by suction and is again forced out from it. The heart, as well as the rest of the vascular system, is of niesoblastic origin and appears close behind the gill-clefts. Like the other large blood-vessels, it is composed of layers, the out«r ( serous >. the middle unuscularK and the inner (epithelium). Hence in origin the heart is a strongly developed blood-vessel. Its complicated structure, such as occurs in the higher vertebrates, is the result of folding and swellings. The heart in the lowest of the vertebrates and in embryonic life is at first divided into two chambers with valves l>e- tween them to prevent the blood from flowing baclavard again. One chamber, the auricle, re- ceives the blood. The other, the ventricle, expels it to the body again. By further modification the sinus voiiosus develops at the venous end and the bulbus arteriosus at the arterial end. Such a condition of heart occurs at some time in the embryonic development of all vertebrates, and it is the permanent condition in many fishes. With the <Ievelopment of lungs, and consequently of the pulmonary artery and veins, the primitive heart is much changed." This change from gilled to hmg-bearing condition may be studied in the embryonic <levelopment of all lung-bearing verte- brates. The heart of fishes is simple, and, in structure, like the primitive heart described. It receives venous blood only, which it forces to the gills. In Dipnoi, where both gills and lungs exist side by side, the heart is half way between that of fishes and amphibia. In amphibia the ventricle is single, and hence the blood in it is uiixed. In many of the amphibia the ventricle is continued into a conus arteriosus, which is spirally twisted and contains a transverse row of valves. Among reptiles an incomplete ven- tricular septum exists in lizards, snakes, and turtles, but there is a complete one in croco- diles. The blood from the right ventricle passes into the pulmonary artery and into the left aortic arch. There are fewer valves in the heart and only one row at the beginning of the aorta and pulmonary artery. In birds and mammals there are two auricles and ventricles — that is to say, auricular and ventricular septa are com- plete. The ventricles are the larger, and have more strongly developed walls. The blood from the head, heart, and body passes into the right auricle. In birds and mammals there is only one aortic arch. In birds it is the fourth right arch which persists, and in mammals the fourth left. In the embrvological development of birds and manmials the auricles are, for a time, in communication through the foramen ovale. Much variation exists among niauuuals in the mode of origin of the carotids and subdavians from the arch of the aorta. In branchial verte- brates the dorsal aorta is formed by the union above the pills of the branchial vessels. The allantois vein, which plays .so important a part in reptiles and .amphibia, is functional in birds and mammals only for a time in embryonic life, Vol. IV.— 4'.i. and from birds onward the hepatic-portal system supplants the renal-portal. The veins of vertebrates are provided with valves to prevent a back flowing of the blood. The IjTiiphatic system of elasmobranchs, am- phibia, and, to some extent, of birds and rep- tiles, is provided with lymph-hearts. In fishes and amphibia there arc large lymph-spaces, but from birds onward lymph-vessels with wcllde- fined trunks are present. The main lymph- vessel is the thoracic duct which empties in mammals into the left and in the Sauropsida into both the right and left branchio-cephalic veins. The lymph-vessels like the veins, are provided with valves which prevent a retlu.x of the lymph- fiuid. The lymph, like the blood, is composed of fluid and corpuscles. Lymphatic tissue oc- curs in fishes and amphibia, but lymph-glands I>roper appear ahmg the course of the lymph- vessels, probably first in birds. In lymphatic tissue or glands the leucocytes, or white cor- puscles of the blood, and lymph develop. BiBLiOGR-^PiiY. Sabatier, Etudes sur le caeur dans la scrie des vertehres (Paris, 1873) ; Mena- gaux, Rccherches sur la cirrulaliun dcs Lamelli- oraiichcs marines (Besancon. 1890) ; Bojanus, "Ueber die Athem- imd Kreislaufwerkzeuge der zweischaligen Muscheln." in Isis (1817. 1820- 1827) : Delage, "Contribution a I'etude de I'ap- pareil circulatoire des crustaces edreophthalmes marines" in Archiie de zoolor)ie expcrimentale. Vol. IX. (Paris. I88I); Cueiiot. "Ktude sur le sang et les glandes lymphatiques dans la serie ani- male," in Archive de zoologie expiri men tale (Paris, 1888-91) ; Muller, "Ueber das Gefiisssys- tem der Fische," in Abhandlungen der Berliner Akademie (Berlin. 1839). See Akatomy, Com- PAK.TIVE; and consult the authorities referred to there. CIR'CUMCEL'LIOIIES (Lat. nom. pi., from cirriim, around + cella, cell ; also called in Jled. Lat. circelliones, by popular etT,iuology.with Lat. circeUus, circlet, dim. of cirmilus, circle). Fa- natical Donatists of the fourth century, who got their name from their habits of wandering. They rambled over the covintrv, plundering, burning houses, and murdering those who made resistance, saying that by such means they sought the crown of martyrdom. They styled themselves ayonistw, wrestlers, or soldiers of Christ, and called their chiefs the leaders of the sons of the Holy One. Constantine treated them with forbearance: but his successors. Con- stans and Constantius. put them down with a strong hand. The name was also applied in the thirteenth century to a sect of fanatical heretics in Swabia, partisans of the Emperor Fred- erick II. CIRCUMCISION (Lat. drcumcisio, from circumcidcrc, to cut around, from circum, around + cfedere. to cut). The cutting away of the foreskin, a religious ceremony practiced !>%• many peoples in difl'crent parts of the world, and going back to the earliest known periods of human history. It is probably a substittite for an original phallic sacrifice. Among many races the custom of cutting oil the phallus of their enemies has prevailed. It is significant that the ancient Egyptians performed this mutilation only in the case of enemies who were circumcised. In order to lie cut off, the phallus must he clean — i.e. fit to be oflered. The purpose of such an offering, presumably to some god of fertility.
