428 FREDERIC T. LEWIS 



cept for reversal, no difference in shape could be observed 

 between the tubules of the opposite sides. The embryo shows 

 thirty-four tubules entering the right Wolffian duct, which is the 

 number credited to this specimen in Doctor Bremer's earlier 

 study. On the left there are thirty-seven tubules, including 

 four of somewhat retarded development at the caudal end. Be- 

 ginning the count anteriorly, the tubule modeled is the twenty- 

 seventh. As calculated from the model, which was made at 

 an enlargement of 500 diameters, the length of the tubule from 

 glomerular capsule to Wolffian duct is 0.3 mm. 



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 service- 

 able in the more complicated later stages in the pig embryo. 



The second model of a human tubule (fig. 6) is from an embryo 

 of 16 mm., excellently preserved and stained with iron haema- 

 toxylin. The tubule selected is from the left Wolffian body, in 

 which there are thirty tubules entering the Wolffian duct, this 

 one being the eighteenth. Presumably it has passed through a 

 stage similar to that in figure 5, but has increased in length from 

 0.3 mm. to 0.8 mm. Although cytological differentiation has 

 advanced, the coiling of the tubule has undergone a slight 

 retrograde movement. Beginning at the glomerular capsule, 

 there is a somewhat constricted neck, as others have frequently 

 noted, and portion C is recognized as the tubulus secretorius 

 of Mihalkovics or tubulus postglomerularis of Nicolas. It is 

 capacious, with wide lumen, and thick walls composed of some- 

 what elongated cells distinctly marked off from one another. 

 These cells have conspicuous terminal bars, a frayed brush- 



