THE WOLFFIAN DUCT AND BODY. 



119 



are observed developing in the bowl of the spoon from mesoblast cells, which 

 presently become entirely enclosed by the end of the tube. Subsequently a second 



so 



Fig. 141. TRANSVERSE SECTION THROUGH THE TRUNK OP A DUCK EMBRYO WITH ABOUT TWENTY-FOUR 



MESOBLASTIC SOMITES. (BalfoUt.) 



am, amnion ; so, somatopleure ; sp, splanchnopleure ; wd, Wolffian duct ; st, segmental tube with 

 peritoneal involution ; ca.v, cardinal vein ; m.s, muscle-plate ; sp.g, spinal ganglion ; sp.c, spinal cord ; 

 ck, notocliord ; ao, aorta ; hy, hypoblast. 



and a third set of tubes become developed in a similar manner, but without perito- 

 neal imaginations, and also open directly into the Wolffian duct. Lastly, other tubes 



Fig. 142. TRANSVERSE SECTIONS OP SHEEP EMBRYOES, SHOWING TWO STAGES IN THE DEVELOPMENT OF 



THE WOLFPIAN BODY. (Bonnet.) 



w.d, Wolffian duct; ^v.b, Wolffian body; p.v, protovertebra ; cl>, noto chord ; n.c, neural canal; 

 am, amnion ; ao, aorta ; i, intestine; y.s, yolk-sac. 



with giomeruli become formed between, and open into those which are already 

 connected with that duct. All these tubes are short and straight when first deve- 

 loped, but afterwards lengthen and become converted into convoluted uriniferous 

 tubes, which, like those of the permanent kidneys, begin in a dilated extremity 

 enclosing a tuft of capillary blood-vessels (glomerulus), which are supplied by 

 branches of the primitive aortas. 



