. Biology. Biology. EXCRETORY SYSTEM OF THE LOBSTER 177 MW to the telson, giving off one pair of large arteries in each somite (Fig. 69). The vascular system thus consists of an arterial system and a great body cavity, which forms a blood sinus, taking the place of a venous system in other ani- mals. The pressure forcing the blood through the gills comes from the constant addition of blood to the body cavity through muscular heart beats, aided by the vacuum produced when the heart is emptied. Movements of the appendages also tend to keep up a constant circulation in the sinuses. THE EXCRETORY
. Biology. Biology. EXCRETORY SYSTEM OF THE LOBSTER 177 MW to the telson, giving off one pair of large arteries in each somite (Fig. 69). The vascular system thus consists of an arterial system and a great body cavity, which forms a blood sinus, taking the place of a venous system in other ani- mals. The pressure forcing the blood through the gills comes from the constant addition of blood to the body cavity through muscular heart beats, aided by the vacuum produced when the heart is emptied. Movements of the appendages also tend to keep up a constant circulation in the sinuses. THE EXCRETORY SYSTEM.—Ex- cretion in the lobster must be comparatively sluggish, for the organs for the purpose are small and poorly placed for active func- tion. This may be due to the fact that the lobster and similar forms are naturally sluggish animals, lying in wait for prey, feeding on carrion, etc., rather than moving about actively in search of food. The nephridia are small flattened coiled organs at the bases of the antennules, and consist of a rather large " bladder': and a small glandular part (Fig. 71). From their characteristic color they are also known as the green glands. The external' openings of the nephridial ducts are on the inner faces of the basal segments (Fig. 68, 3). Some excretion of waste matters may also take place through the skin. THE MUSCULAR SYSTEM.—The muscles of the lobster are. FIG. 72.—The abdominal musculature of the lobster to show the complicated arrange- ment of extensors and flexors. (From Gerstaecker, after Milne- Edwards.). Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Calkins, Gary N. (Gary Nathan), b. 1869. New York, H. Holt and company
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