. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 698 CONCHIFERA. going any glandular elaboration, the fluids ab- sorbed to the general current of the circulation. After having thus had all the nutritious ele- ments it contains abstracted, the alimentary mass, having reached the rectum, there com- monly presents itself under the form of minute globules; it is soon afterwards expelled through the anus. Organs of circulation.—The organs of cir- culation in the acephalous Mollusca consist of two vascular systems forming together a simple circuit, namely, a ventricle and an
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 698 CONCHIFERA. going any glandular elaboration, the fluids ab- sorbed to the general current of the circulation. After having thus had all the nutritious ele- ments it contains abstracted, the alimentary mass, having reached the rectum, there com- monly presents itself under the form of minute globules; it is soon afterwards expelled through the anus. Organs of circulation.—The organs of cir- culation in the acephalous Mollusca consist of two vascular systems forming together a simple circuit, namely, a ventricle and an arterial system, and a venous system and two auricles. The ventricle in the majority of acephalous mollusca is single, symmetrical, situated in the dorsal median line of the body, and rests upon the rectum, which it embraces in its evolution (g, Jig. 347, h,fig. 348) on every side so closely, that the intestine appears to pass through it. It is to be presumed, however, that the intestine does not pass im- mediately athwart the heart, but that this canal is only embraced so intimately by the central organ of the circulation, that it is impossible to separate without tearing them. The ventricle, which is regular and symmetrical in the greater number of the genera (a, Jig. 349) is irregular and unsymmetrical in the Ostracean family, (a, Jig. 350). It is generally elongated and fusiform; Figs. 349 & its parietes are thin, formed of muscular fibres variously interlaced, and often projecting in- ternally. From either extremity issues one of the two main arteries of the body, the one superior giving branches to the whole of the anterior parts of the animal; the other pos- terior supplying branches to the principal vis- cera,—the stomach, liver, intestinal canal, and ovary. Many superficial branches penetrate the mantle, and may be observed ramifying more especially upon the thicker parts which constitute its edges. When the back of the animal is very broad, and as a ne
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