. Outlines of the comparative physiology and morphology of animals. Anatomy, Comparative; Physiology, Comparative. BLOOD SYSTEM. 409 ings on the sides of the heart by which blood may be taken in. The diagram (Fig. 287) is an attempt to rep- resent schematically the general course of the circula- tion. The dotted lines represent the lacunary circula- tion without definite vessels. The difference between this lacunary circulation and a true vascular circulation may be illustrated by an irri- gation system. The circula- tion of vertebrates may be compared to a pump and a sys- tem of pipes closed
. Outlines of the comparative physiology and morphology of animals. Anatomy, Comparative; Physiology, Comparative. BLOOD SYSTEM. 409 ings on the sides of the heart by which blood may be taken in. The diagram (Fig. 287) is an attempt to rep- resent schematically the general course of the circula- tion. The dotted lines represent the lacunary circula- tion without definite vessels. The difference between this lacunary circulation and a true vascular circulation may be illustrated by an irri- gation system. The circula- tion of vertebrates may be compared to a pump and a sys- tem of pipes closed through- out and impermeable until the soil to be irrigated is reached and there permeable. After use the overplus of liquid is again gathered into imperme- able pipes and returned to the pump to be again used. The circulatory system of an in- sect, on the contrary, is like a pump with short pipes dis- charging on the soil in front and sucking up from the soil behind. But the soil, instead of being penetrated in all di- rections by pipes which con- fine and guide the currents, is covered with little pools connected by channels. Under these conditions the water would work around in an in- definite way, and be sucked up behind, to be used again. Respiratory System.—Now, it is this peculiar mode of circulation that compels the very exceptional kind of respiratory apparatus. Insects are active, and somewhat warm-blooded animals, and therefore require a perfect aeration of the blood; but with a lacunary cir-. FlG. 288.—Tracheal system of an insect: sp sp, spiracles ; s s, air 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 LeConte, Joseph, 1823-1901. New York, D. Appleton and Company
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