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Fig. 8. Diagram of the double-spiral stage

Diagram of the double-spiral stage, shown in figure 5, with its subdivision into segments C, U, and Z.

For purposes of description this double-spiral tubule may be divided into three parts, as shown in the diagram, figure 8. Beginning with the capsule, there is a portion which may be designated C, this letter suggesting its shape. It curves laterally and dorsally and passes into the lateral arm of a portion named U , the letter again suggesting the form. Finally, the medial limb of the part U ends in another simple C-shaped curve, which, as it is the terminal portion, may be designated Z. This swings laterally to end in the Wolffian duct which at this early stage is both lateral and dorsal. The rather cumbersome subdivision of the tube into C, U, and Z portions will prove especially serviceable in the more complicated later stages in the pig embryo.


Lewis FT. The course of the Wolffian tubules in mammalian embryos. (1920) Amer. J Anat. 26(3): 423-436.

Cite this page: Hill, M.A. (2024, February 28) Embryology LewisFT1920 fig08.jpg. Retrieved from

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© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G

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