Elementary Zoology by Vernon L. Kellogg

Author:Vernon L. Kellogg [Kellogg, Vernon L. (Vernon Lyman)]
Language: eng
Format: epub
Published: 2016-07-31T00:00:00+00:00

The cavity thus exposed is the pericardium. Note within the pericardium a long tube extending through it. This is a portion of the alimentary canal, the rectum, which opens posteriorly through the anus into the supra-branchial chamber. Note a muscular sac about the rectum midway of its course through the pericardium. This is the unpaired ventricle of the heart. Attached to each side of the ventricle are thin-walled sacs, the right and left auricles, which are entered by fine blood-vessels, the efferent branchial veins, from the right and left gills. The blood brought through these blood-vessels from the gills flows into the auricles and from them into the unpaired muscular ventricle, from which it is forced anteriorly and posteriorly through two main arteries, the anterior and posterior aortas, to all parts of the body. After bathing the body-tissues the blood is collected into a median longitudinal vein beneath the pericardium called the vena cava. From the vena cava the blood passes through the kidneys and gills to be returned at last to the heart. The mantle acts as an organ for the aeration of the blood, and the blood it receives or at least part of it passes directly back to the heart without passing through the kidneys and gills.

Note the delicate membranous dark-colored sac on the floor of the pericardium, the kidneys or nephridia. These are paired structures which appear as two U-shaped tubes lying side by side. Each consists of a lower portion with thick folded walls, the kidney proper, and an upper thin-walled portion, the ureter. The kidneys open internally through a pair of reno-pericardial openings into the pericardium, while the ureters communicate with the mantle-cavity by an opening on the side of the body beneath the gills as already mentioned. The kidneys are profusely supplied with fine blood-vessels and carry off the waste matter from the blood.

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