WOLFFIAN TUBULES IN MAMMALIAN EMBRYOS 429 



border, a superficial granular zone not deeply stained, and a still 

 paler basal zone containing the oval nuclei. In a typical manner 

 they show the histological features of secretory activity which 

 cannot be reconciled with Gadow's opinion that "the Wolffian 

 body in birds and mammals appears never to function, not even 

 in the embryo." 1 



In the 16-mm. embryo, the segment U may be considered to 

 begin where the tubule becomes abruptly narrower, with a corre- 

 sponding radical change in the histological nature of its walls. 

 The lumen is narrower, and the cells which are longer, with less 

 cytoplasm, stain deeply with iron haematoxylin. The portion 

 U is therefore a subdivision of the tubulus collectivus of Mihal- 

 kovics or tubulus terminalis of Von Winiwarter. Whatever its 

 function, it must be very different from that of the preceding 

 part. With certain minor swellings and constrictions, the portion 

 U makes the bend and passes gradually into Z. As the Wolffian 

 duct shifts ventrally, this terminal part of the tube has become 

 longer and more curved. Sometimes, as noted by Felix, it does 

 not remain in the same horizontal plane with the rest of the 

 tubule, but may bend either anteriorly, as in the figure, or 

 posteriorly. 



In an older embryo — 22.8 mm., figure 7 — certain tubules are 

 much longer than before, though degeneration of the Wolffian 

 body has become active. Felix found that from the stage of 

 21 mm. onward, the Wolffian tubules are "almost all broken in 

 one or several places," notably at the neck of the glomerular 

 capsule, at the junction of the secreting and collecting portions, 

 and at the outlet into the Wolffian duct, and that "all degenerat- 

 ing tubules show a tendency to lose to a greater or less extent 

 their S-shape." The tubule here modeled appeared to be intact 

 throughout, though at this stage they are so difficult to follow 

 that errors are quite possible, either in introducing a disconti- 

 nuity or in filling an actual gap. The tubule chosen for modeling 



1 This statement is found on page 829 of Bronn's Klassen und Ordnungen des 

 Thier-Reichs, Bd. 6, Abth. 4, Vogel, von H. Gadow and E. Selenka. It appears 

 to be in Gadow's portion of the work and is wrongly credited to Selenka by Weber, 

 who among others, accepts it. See Weber, In Schwalbe's Archiv, 1897, page 621. 



