238 



STUDY OF PIG EMBRYOS. 



be differentiated. By a secondary process these tubules are supposed to become 

 united with the branches from the renal pelvis, the branches forming only the 

 collecting tubules of the adult organ. According to another view, the condensed 

 tissue is partly mesenchyma and partly an outgrowth from the walls of the renal 

 epithelium. This interpretation makes the collecting tubules arise as branches 

 of the pelvis, and the convoluted tubules and glomeruli as branches of the collect- 

 ing tubules. The origin of the renal anlage may easily be followed in earlier stages. 

 It is found that from the pelvic end of each Wolffian duct there develops a dorsal 



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Fig. 138. — Pig, 17.0 mm. Transverse Series 51, Section 759. 

 All, Allantois. Ao, Aorta. A.am, Umbilical artery, card. Branch of cardinal vein. Cat, Ccelom. G, Gan- 

 glion. A'i, Kidney. N', N", Nerves. Nch, Notochord. P.L, Posterior limbs. Rtct, Large intestine. Sp.c, 

 Spinal cord. Sym, Sympathetic ganglion. W.b, Wolffian body. W.D, Wolffian duct. X '7 diams. 



outgrowth, which is lined by epithelium. This outgrowth elongates in a head ward 

 direction. Its end expands; the narrow portion is the ureter, the expanded por- 

 tion the anlage of the pelvis. The pelvis becomes irregular in shape and forms 

 outgrowths. Around it appears the condensed tissue just referred to. On the 

 ventral and lateral sides of the kidneys in our section appear the ends of the 

 Wolffian bodies, W. b. From the ventral and inner edge of each Wolffian body 

 is a projecting lobe of tissue in which the Wolffian duct, II*. D, is lodged. The 

 walls of the Wolffian duct are a rather thin, cuboidal epithelium, surrounded by 



