. The development of the chick; an introduction to embryology . ephric tul)ules. n. T., Xephr()r. may also be detected in the female (p. 401). It is diflicult tostate the exact period of beginning and cessation of function ofthe mesonephric tubules. Judging from the histological appear- FiG. 218. — Profile reconstruetion of part of (he Wolffian duct and primordiaof mesonephric tubules (rei)resented by cireles) of a duck emliryo of 45somites. (After Schreiner.)XXIV, XXV, etc., position of the corresponding somites. Lines 114 A, 114 B, 114 C, represent the positions of the sections shown in thes
. The development of the chick; an introduction to embryology . ephric tul)ules. n. T., Xephr()r. may also be detected in the female (p. 401). It is diflicult tostate the exact period of beginning and cessation of function ofthe mesonephric tubules. Judging from the histological appear- FiG. 218. — Profile reconstruetion of part of (he Wolffian duct and primordiaof mesonephric tubules (rei)resented by cireles) of a duck emliryo of 45somites. (After Schreiner.)XXIV, XXV, etc., position of the corresponding somites. Lines 114 A, 114 B, 114 C, represent the positions of the sections shown in these figures. 382 THE DEVELOPMENT OF THE CHICK ances, however, it is pn)l)al)le that secretion begins in the tubuleson the fifth (hiy and increases in amount up to tlie eleventh dayat least, when signs of degeneration become numerous. Presuma-bly the functional activity diminishes from this stage on, beingreplaced by the secretion of tlie i)ermanent Fig. 220. — Tnmsverse section tlirouf:;h the mesonephrosand neighboring parts of a G-day chick, in the n^gion ofthe , Aorta. 1), IMood vessels (siinisoids). Caps., Cap-sule of renal corpuscle. Coel., Coelouie. col. T., Collectingtubule. 1)., (liz., (lizzard. Cloin., (Jlonierulus.(ion., (ioiiud. I>., I>eft. Spl., Spleen. Sr. C, Cortical sub-stance of the suprarenal, s. t., Secreting tubule. T. R.,Tui)al ridge. V., Ventral. V. c. p., Posterior cardinal veinV. sc. 1., Left subcardinal vein. \N. ])., WollHan duct. Figs. 220 and 221 represent seel ions thiough Ihe nusonephroson the and eightli days respectively (see also Fig. 222,eleven days). The renal corpuscles show the typical capsuleand gloincruhis, and relation to the secreting tubules. The latterare considerably convoluted on the sixth day, nuich more so onthe eighth day. The conducting tubules can usually be distin-guished by their smallcf caliber and thiinier walls. The Wolffian THE URINOGENI
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