. Animal forms; a second book of zoology. Zoology. THE WORMS 57 means of the fluid in the body cavity ; but in the earthworm the division of labor between different parts of the body is more perfect, and a definite blood system now acts as a distributing apparatus. This consists primarily of a dorsal vessel lying along the dorsal surface of the alimentary ('anal (Fig. 34), from which numerous branches are given off to the body wall, and to the digestive system through which they ramify in every direction before again being collected into a ventral vessel lying below the digestive tract. In som
. Animal forms; a second book of zoology. Zoology. THE WORMS 57 means of the fluid in the body cavity ; but in the earthworm the division of labor between different parts of the body is more perfect, and a definite blood system now acts as a distributing apparatus. This consists primarily of a dorsal vessel lying along the dorsal surface of the alimentary ('anal (Fig. 34), from which numerous branches are given off to the body wall, and to the digestive system through which they ramify in every direction before again being collected into a ventral vessel lying below the digestive tract. In some of the anterior segments a few of the connecting vessels are muscular and unbranched, and during life pul- sate like so many hearts to force the blood over the body, forward in the dorsal vessel, through the " hearts " into the ventral vessel, thence into the dorsal by means of the small connecting branches. Some of the duties of this vascular system are also shared by the fluid of the body cavity, which is made to cir- culate through openings in the parti- tions by the contractions of the body wall of the animal in the act of crawl- ing. In this rough fashion a consider- able amount of nutritive material and oxygen are distributed to various or- gans, and wastes are carried to the kid- neys to be removed. 58. Excretion.—In nearly all of the. segmented worms there is a pair of Fig. 85.—Diagram of earth- worm kidney. 6, blood- vessel ; /, funnel open- ing into body cavity ; o, outer opening; s, septum ; u\ body wall. kidneys to every segment (Figs. 34, 35). Each consists of a coiled tube wrapped in a mass of small blood-vessels, and at its inner end communicating with the body cavity by means of a funnel-shaped opening. In some unknown way the walls of the kidney extract the waste materials from the blood-vessels coursing over it and pass them into its tubular cavity. At the same time the cilia about the mouth of the funnel-shaped extremity are. Please note that
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