WOLFFIAN TUBULES IN MAMMALIAN EMBRYOS 



425 



to these designations Nicolas and Von Winiwarter have taken 

 exceptions. 



Of greater interest perhaps, and not open to question, is the 

 finding by Mihalkovics that in the sheep the middle or transverse 

 limb of the S elongates and becomes itself S-shaped, though the 

 long axis of the second S is horizontal, being at right angles with 

 that of the first. "Here in a narrow space," according to Mihal- 

 kovics, "a winding-up process takes place," which leads to a 

 double or reversed spiral, as shown in figures 3 and 4. Mihal- 

 kovics did not follow the further development of this pattern. 



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Fig. 1 Section of an S-shaped Wolffian tubule. Rabbit embryo, 10i days, 

 5.4 mm. Harvard Embryological Collection, series 560, sections 158-161. X 200. 



Fig. 2 Diagram of the S-shaped tubule. 



Fig. 3 Diagram of the double-spiral tubule. 



Fig. 4 Section of a double-spiral tubule. Pig embryo, 4.5 .mm. Harvard 

 Embryological Collection, series 1404, sections 114-115. X 200. 



Gl., glomerular capsule; W.d., Wolffian duct. 



In 1890 Meyer described the simple S-stage in man, and in 1902, 

 with a wealth of lithographs, Schreiner repeated the observations 

 of Mihalkovics on the early stages in the lizard, duck, and chick, 

 with the rabbit in place of the sheep. He refers to the double 

 spiral pattern as a 'much-coiled S,' but there is nothing to suggest 

 that he regarded it as a particularly significant form, essentially 

 different from the simple S. Minot, in 1892, in an account based 

 upon Mihalkovics, notes that the tubules of amniota "retain for 

 some time their simple S-shape, although the curves of the S 

 become more and more exaggerated." These appear to be the 



