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. 
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., Seereting tubule. T. R., 
Tubal ridge. V., Ventral. V. e. p., Posterior cardinal vein 
V.s’e. 1., Left subeardinal vein. W. D., Wolffian duct. 
Figs. 220 and 221 represent sections through the mesonephros 
on the sixth and eighth days respectively (see also Vig. 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 
