. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. , Nerve Cord Notochord "—Dorsal Aorta ^"Cardinal Vein ^Glomerulus Intestine Fig. 373. Cross section diagram showing pronephridial stage of the excretory system. Successive glomeruli frequently fuse into a single, elongate capillary-mass, known as a glomus (See Fig. 374). join together, down each side of the body, to form a common segmental, or pronephric, duct. This duct is eventually extended posteriorly, mainly by additions from the coelomic wa
. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. , Nerve Cord Notochord "—Dorsal Aorta ^"Cardinal Vein ^Glomerulus Intestine Fig. 373. Cross section diagram showing pronephridial stage of the excretory system. Successive glomeruli frequently fuse into a single, elongate capillary-mass, known as a glomus (See Fig. 374). join together, down each side of the body, to form a common segmental, or pronephric, duct. This duct is eventually extended posteriorly, mainly by additions from the coelomic wall, to open into the cloaca. On the opposite side of the nephrocoele from the nephrostomes a capil- lary ridge, the glomus, forms along the coelomic wall (Figs 373 and 374), so that there are two methods of obtaining excretory products from the blood. They can pass first by diffusion into the general body cavity and then into the nephrocoeles or they can go directly from the capillaries of the glomus into the nephrocoele. In either instance the liquid excretory material is passed on through the ciliated nephrostomes and pronephridia to the segmental ducts, which dispose of the waste to the outside. No encapsuling connective tissue, like the tunica fib- rosa of the human kidney, surrounds and unifies the pronephridia into a definite organ. The pronephroi are best developed in cyclostomes, where in some species they persist throughout life, al- though replaced functionally in most cases by mesone- phroi or kidneys of the second order. It is probable that in some myxinoids, Polistotrema or Bdellostoma, for example, they remain as the lifelong functional kidneys. They also persist. Fig. 374 struction pronephros Salamandra, Recon- of the of a, aorta; c, coelom; d, pronephric duct; g, glomus; 1, 2, 3, pronephridia. (Af- ter Kingsley; Se- mon.). Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and
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Keywords: ., bookcentury1900, booksubjectanatomycomparative, booksubjectverte
