EXPLANATION OF PLATES. 



PLATE 1. 



FIG. 1. Embryo pig 9 nun. long (about the stage of fig. 12 in Kcibel's Xonnaltafcln, Das Schweini, in which tin- 

 veins of the right Wolffian body have been injected with silver nit rale. This is a stage before the tail 

 has curved and hence the specimen is younger than the one of fig. 2, which measures less. Cleared by 

 the Spalteholz method. Xll. v. c., v. caudalis; v. c. M., v. cardinalis mesialis at the point at which 

 it curves dorsalward to join the v. cardinalis posterior; v. c. p., v. cardinalis posterior; v. T. L., v. trans- 

 versa lateralis of the Wolffian body; v. T. M., v. transvevsa mesialis of the \VolfIian body; v. v., v. ven- 

 tralis of the Wolffian body. 



2. Dissection of an embryo pig 8 mm. long, in which the veins have been injected with silver nitrate through 



the anterior cardinal vein. The left Wolffian body has been dissected away so that the mesial surface 

 of the right Wolffian body is exposed. Cleared by the Spaltchol/, method. Xll. v. c. P., v. cardinalis 

 posterior; v. c. M., v. cardinalis mesialis at the point of the anastomosis of the veins of the two sides, 

 which is also the point where the v. cardinalis mesialis dextra curves ventralwanl to the liver; v. M. A., 

 v. mesialis anterior of the Wolffian body; v. OM., oniphalo-mcsenterica ; v. s., v. spinalis; v. T. M., 

 v. transversa mesialis <>f the Wolffian body; v. u., v. umbilicalis; v. v., v. ventralis of the Wolffian body. 



3. Embryo pig 11 mm. long, in which the veins have been injected with silver nitrate, showing the left Wolffian 



body and through it the right mesial cardinal vein. Cleared by the Spalteholz method. Xll. v. c. M.. 

 v. cardinalis mesialis; v. c. p., v. cardinalis posterior; v. F. P., v. fibularis primitiva; v. T. M., v. trans- 

 versa mesialis belonging to the left Wolffian body; v. T. L., v. transversa lateralis of the Wolffian body; 

 v. u., v. umbilicalis; v. v., v. ventralis of the Wolffian body. 



-1. Dissection of an embryo pig 23 mm. long, in which the veins have been injected with silver nit rate. Cleared 

 by Spalteholz method. X10. D. c., ductus Cuvier; v. A., v. azygos; v. A'., v. azygos above the 1 point 

 where it is joined by the v. cardinalis posterior; v. c. P., v. cardinalis posterior; v. c. v'., v. cardinalis 

 posterior within the Wolffian body; v. I., anastomosis which is the forerunner of the v. innominata; 

 v. M. A., v. mesialis anterior of the Wolffian body; v. M. I., v. mammaria interna; v. TE., v. thoraco- 

 epigastrica; v. T. L., v. transversa lateralis making the mainroot of the vena cava within the Wolffian 

 body; v. u. p., v. ulnaris primitiva; v. v., v. ventralis of the Wolffian body; w. B. i., Wolffian body, 

 inner gloinerular zone. 



PLATE 2. 



5. Embryo pig 22 mm. long, in which the veins have been injected with silver nitrate, and the entire embryo 



cleared by the Spalteholz method. Xll. v. A., v. azygos; v. B., common stem of the v. fibularis 

 primitiva and the v. caudalis which empties into the median mesonephritic vein and which becomes the 

 lower segment of the vena cava inferior; v. c., v. caudalis; v. c. A., v. cardinalis anterior or v. jugularis 

 interna; v. c. P., v. cardinalis posterior; v. c. i., v. cava inferior; v. F. p., v. fibularis primitiva; v. J. E., 

 v. jugularis externa; v. L. T., v. lumbahs transversa; v. M. i., v. mammaria interna; v. T. L., v. trans- 

 versa lateralis of the Wolffian body making the main roots of the vena cava; v. TE., v. thoraco-epigas- 

 trica; v. u. p., v. ulnaris primitiva; w. B., Wolffian body. 



PLATE 3. 



6. Transverse section of an embryo pig 9.5 mm. long in which the entire vascular system has been injected 



with India-ink through the umbilical artery. The section is unstained and is 250 M thick. It passes 

 through the lower half of the Wolffian body and is to be compared with fig. 2. X36. A., aorta; o. s., 

 position of a ganglion spinale; v. c. P., v. cardinalis posterior; v. c. M., v. cardinalis mesialis; v. T. M., 

 v. transversa mesialis of the Wolffian body, connecting the v. cardinalis posterior with the v. cardinalis 

 mesialis; v. T. v., v. transversa ventralis of the Wolffian body, the leader being at the position of the 

 v. ventralis at a little later stage; v. s., v. spinalis; v. u., v. umbilicalis; w. D., Wolffian duct. 



7. Dissection of an embryo pig 14 mm. long in which the vascular system has been injected with India ink 



through the umbilical artery. The left Wolffian body has been removed, the right one is in place. X20. 

 A. s., a. spinalis; D. c., ductus Cuvier; P. P., prevertebral plexus of veins from the body-wall and from 

 the spinal cord entering the Wolffian body in a sagittal plane lateral to the v. hemiazygos, the lower 

 part of which plexus becomes a prevertebral caval plexus; v. A., v. azygos in the form of its antecedent 

 capillary plexus; v. M. I., v. mammaria interna; v. j. E., v. jugularis externa; v. TE., v. thoraco- 

 epigastrica. 



8. Transverse section of an embryo pig 13.5 mm. long in which the vascular system has been injected with 



India-ink through the umbilical artery. The section passes through the cephalic half of the Wolffian 

 body and is to show the prevertebral capillary plexus in which the v. azygos and the v. hemiazygos 

 develop. The section is unstained and is 250 M thick. It is about the stage of the specimen in fig. 7. 

 X40. A., aorta; A. s., a. spinalis; P. v. A., plexus in which the vena azygos develops; v. u ., vein of the 

 body-wall; v. TE., v. thoraco-epigastrica; v. s., v. spinalis; v. T., v. transversa of the Wolffian body; 

 x., plexus of capillaries lateral to the myotome. 



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