. A manual of elementary zoology . Zoology. 502 MANUAL OF ELEMENTARY ZOOLOGY disappears altogether. The fourth branchial arch becomes the pulmo-cutaneous. It loses its connection with the aorta save for a vestige in the form of a ligament in most adults, but sometimes, as always in the newt, an open connection persists, and is known as the ductus We have seen (p. 449) that it is present also during the development of the rabbit, where a vestige remains in the Fig. 382. —Diagrams of the development of the excretory system of the frog.—From Bourne. A, The system of a tadpole
. A manual of elementary zoology . Zoology. 502 MANUAL OF ELEMENTARY ZOOLOGY disappears altogether. The fourth branchial arch becomes the pulmo-cutaneous. It loses its connection with the aorta save for a vestige in the form of a ligament in most adults, but sometimes, as always in the newt, an open connection persists, and is known as the ductus We have seen (p. 449) that it is present also during the development of the rabbit, where a vestige remains in the Fig. 382. —Diagrams of the development of the excretory system of the frog.—From Bourne. A, The system of a tadpole about 12 mm. long, showing the pronephros and origin of the mesonephric tubules ; B, the system at the end of metamorphosis. The broken line represents approximately the position of the strip of peritoneal epithelium which gives rise to the oviduct. c/., Cloaca; , dorsal aorta ; , fat body ; glomerulus l£". genital ridge ; mes., mesoneDhros ; , mesonephric tubules ; oviduct; pzj/T, position of oviducal opening; ^ pronephric funnels ; pnp.^ pronephros ; segmental duct. The first rudiment of the excretory system appears some time before hatching as a longitudinal thicken- exoretory and ing of the somatic layer of mesoblast on each ; side of the body, at the front end of the peri- toneal cavity, immediately below the myotonies. The front part of this thickening becomes converted into the head kidney or pronephros (p. 354), which consists of three twisted tubules, each opening by a funnel into the 1 The terms ductus Botalli and ductus arteriosus are often used as equivalent to one another, each being applied to both of the little vessels which complete the carotid and pulmonary 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 Borradaile, L. A. (
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectzoology, bookyear1920
