382 



THE DEVELOPMENT OF THE CHICK 



ances, however, it is probable that secretion begins in the tubules 

 on the fifth day and increases in amount up to the eleventh day 

 at least, when signs of degeneration become numerous. Presuma- 

 bly the functional activity diminishes from this stage on, being 

 replaced by the secretion of the permanent kidney. 



SrCr^ 



Gem . '';>' ? • ■ '> 



Fig. 220. — Transverse section through the mesonephros 



and neighboring parts of a 6-day chick, in the region of 



the spleen. 



Ao., Aorta, bl. V., Blood vessels (sinusoids). Caps., Cap- 

 sule of renal corpuscle. Coel., Coelome. col. T., Collecting 

 tubule. D., Dorsal. Giz., Gizzard. Glom., Glomerulus. 

 Gon., Gonad. L.,Left. Spl., Spleen. Sr. C, Cortical sub- 

 stance of the suprarenal, s. t., Secreting tubule. T. R., 

 Tubal ridge. V., Ventral. V. c. p., Posterior cardinal vein 

 V. s'c. 1., Left subcardinal vein. W. D., Wolffian duct. 



Figs. 220 and 221 represent sections through the mesonephros 

 on the sixth and eighth days respectively (see also Fig. 222, 

 eleven days). The renal corpuscles show the typical capsule 

 and glomerulus, and relation to the secreting tubules. The latter 

 are considerably convoluted on the sixth day, much more so on 

 the eighth' day. The conducting tubules can usually be distin- 

 guished by their smaller caliber and thinner walls. The Wolffian 



