Susanna Phelps Gage 419 



pad nearly through the region of the leg-pad, and of Wolffian ducts 

 opening into the cloaca. Sections of the ridges and their contained 

 structures are shown at different levels, beginning cephalad, in Figs. 11, 

 18, 10, 19, 6, 20, and 5. 



There is no definite thickening in the ccelomic epithelium or the meso- 

 derm which can be designated as a rudiment of the genital ridge or of the 

 Miillerian duct. 



In the ridges, the Wolffian duct is traceable as indicated by dots in 

 Fig, 17 from the 1st mesonephric tubule along the lateral border of the 

 ridge and extending beyond the coelom in a curve (Fig. 5), to open into 

 the lateral border of the cloaca (Fig. 17). Extending still farther 

 laterad along the Wolffian ridge is the cardinal vein, the diameter of which 

 varies greatly in different sections (Figs. 18, 19). 



Adrenal. — ISTear the cephalic end of the Wolffian ridge (Figs. 17, 11, 

 suprarenal), on the mesenteric border are slight folds in the epithelium 

 which remind one of the structures in the cephalic part of the meso- 

 nephros found by Aichel " in the rabbit to be associated with the develop- 

 ment of the adrenal or suprarenal body. 



Pronephros. — A wide open funnel (Figs. 17, 18), opening to the 

 coelom and connecting with a small, l)lind tube extending cephalad for a 

 few sections, is here called a pronephric tubule on account of its position 

 in the cephalic portion of the Wolffian ridge. It has no connection 

 whatever with the Wolffian duct and is separated by a marked interval 

 from the beginning of that duct. This is apparently only a further 

 retrogression from the condition found by MacCallum ^' in which a 

 separated portion of duct extends opposite the 6th, 7th, and 8th myotomes 

 of an embryo 3.5 mm. long. MacCallum calls attention to the possibility 

 that this separated tube with its cephalic opening through a funnel to the 

 coelom may be a pronephric remnant. In an older embryo (5 mm. long) 

 he finds such a disconnected remnant with a single tubule not opening 

 to the coelom. 



Tandler'* says that in human embryos from 5 to 20 mm. he found 

 pronephric tubules in communication with the coelom eight times. These 

 were at the level of the 5th to 6th segment. 



In Embryo 148, the isolated pronephric tubule lies opposite the 11th 

 myotome. Whether the difference in position relative to the myotomes 

 from those reported by MacCallum and Tandler, indicates that this is not 



" Aichel, Otto, Arch. f. mlkr. Anat.. LVI, 1900. 

 "MacCallum, J. B., Amer. Jour. Anat., I, 1902. 

 "Tandler, J., Centralbl. f. Physiol., XVIII, 1904. 



