. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. Cuttle-fah. the gills has a dilated contractile portion (£>*), which dilatations may be considered as bran- chial hearts, so that there are three separate contractile portions of the circulatory system. In the Gasteropoda and Pteropoda, there is only one heart. This organ is strong and mus- cular, provided with valves, and consisting of an auricular and a ventricular cavity (Jigs. 321 and 322, h, H). In the Testaceous Acephala, the heart is nearly of the same structure as in the orders just mentioned, but less fully d
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. Cuttle-fah. the gills has a dilated contractile portion (£>*), which dilatations may be considered as bran- chial hearts, so that there are three separate contractile portions of the circulatory system. In the Gasteropoda and Pteropoda, there is only one heart. This organ is strong and mus- cular, provided with valves, and consisting of an auricular and a ventricular cavity (Jigs. 321 and 322, h, H). In the Testaceous Acephala, the heart is nearly of the same structure as in the orders just mentioned, but less fully deve- loped. In most of them, as also in the Gas- teropodous Mollusca, the rectum passes through the ventricle. The auricle is occasionally double. The Brachiopoda have two aortic hearts, but of a very simple structure, not being divided into auricular and ventricular portions. The naked Acephala, such as the Ascidise, have the simplest heart of all the Mollusca, consisting of a thin membranous ventricle apparently without valves. In all these animals, the course of the blood is generally considered to be the following: Arterial blood only passes through the systemic or aortic heart (or hearts where this organ is double), and is carried to the system by the branches of the systemic arteries (A, «). The VOL. I. altered blood, returning in the veins of the system, is collected into one or more trunks ( F), and carried in the subdivided branches of these (fig. 321, jig. 322, JB) to the re- Fig. Helix. spiratory organ, which consists of branchial plates or fringes in the greater number, but in some of the Gasteropoda, as in the Garden- Snail, of pulmonary sacs. In most cases, the whole of the blood returning from the system passes through the respiratory organ. In others, especially in some Bivalves, the vena cava or systemic veins send branches directly to the auricle as well as to the gills. In the compound Ascidise, Mr. Lister* has recently discovered one of the most rem
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