. The development of the chick; an introduction to embryology . Fig. 222. — Transverse section through the metanephros, mesonephros,gonads and neighboring structures of an 11-day male chick,a. A. S., Abdominal air-sac. Ao., Aorta. B. W., Body-wall. Coel., Coe-lome. Giz., Gizzard. II., Ilium. M. D., Remains of degenerating Miillerianduct. Mst., Mesentery. Mtn., Metanejihros. Sp., Spine of neural arch,tr^ Pr., Transverse process of the neural arch. V. c. i., Vena cava D., Wolffian duct. Other abbreviations as before. 386 THE DEVELOPMENT OF THE CHICK. Fig. 223. — Trofik reconstruction
. The development of the chick; an introduction to embryology . Fig. 222. — Transverse section through the metanephros, mesonephros,gonads and neighboring structures of an 11-day male chick,a. A. S., Abdominal air-sac. Ao., Aorta. B. W., Body-wall. Coel., Coe-lome. Giz., Gizzard. II., Ilium. M. D., Remains of degenerating Miillerianduct. Mst., Mesentery. Mtn., Metanejihros. Sp., Spine of neural arch,tr^ Pr., Transverse process of the neural arch. V. c. i., Vena cava D., Wolffian duct. Other abbreviations as before. 386 THE DEVELOPMENT OF THE CHICK. Fig. 223. — Trofik reconstruction of the Wolffianduct and priniordiuni of the metanephros of achick embryo of G (hiys and S hours. (AfterSchreiner.) XXV to XXXHI, twenty-fifth to tliirty-thirdsomites. Al. N., Neck of jiUantois. CL, , Intestine. Msn., n. T.,Nephrof^enous tissue of the metanephros includedwithin the dott(>d lines. W. D., Wolffian , Ureter. THE URINOGENITAL SYSTEM 387 omoiis manner, and it is from them tliat the collecting tubulesof the kidney arise; the posterior unbranched portion of the meta-nephric diverticulum represents the tlefinitive ureter. The following data concerning these branches should be noted: (1) the first ones are formed from the posterior portion of themetanephric diverticulum, and the process progresses in ananterior direction. This is the reverse direction of the usual orderof embryonic differentiation, but the reason for the order is thesame, viz., that differentiation begins in the first formed parts. (2) A po
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