3G Develo])inent and Shape of Uriniferous Tubules 



whole structure acquiring a lumen and the S-shaped stage of the tubular anlage is 

 reached. Herring states that " By active proliferation of cells, the vesicle grows in 

 length, but not as a straiglit tube ; it becomes comma-shaped, the bend of the comma 

 being always away from the collecting tubule with whicli it eventually joins." " The 

 comma is now in close contact with the ampulla, but the lumens are not continuous. 

 As the comma-shaped body grows, it elongates, but the tail remains in the same posi- 

 tion ; further growth is upward toward the capsule along the end of the collecting 

 tube. It grows more quickly than the latter and takes on another curve at its upper 

 end. this time toward the ampulla. The result is an S-shaped body, with centra! 

 lumen. When the S is well developed, its lumen becomes continuous with the lumen 

 of the collecting tube." In both of these accounts, the anlage of the lower curve of 

 the future S-shaped structure, as above given, is missed. Hamburger states that 

 when the anlage of the coiled uriniferous tubule lias reached a diameter of 40 m to 50 m > 

 a small cavitv develops in its center (renal vesicle) and shortly after this, a union 

 between it and the ampulla is established and a short solid cord of cells, which extends 

 from the peripheral end of the ampulla to the lateral wall of the vesicle develops. 

 In Its further development, the tubular anlage obtains a depression, always seen on 

 the side of the anlage which is turned away from the ampulla with which it is con- 

 nected ; its wall sinks in somewhat, thus giving the cavity the form of a " half-moon 

 shaped cleft ; " this depression deepens and develops into a cleft and there is formed 

 a " wing-like process," which lies against the side of the anlage and terminates with 

 a sharp free border, which projects toward the surface of the kidney. When the 

 anlage of the coiled uriniferous tubule has attained the size of 50 m- to 60 /j. it still 

 has a spheric shape" but consists of 1, a bowl (Schale), the concavity of which 

 is turned toward the surface of the kidney. 2, a short thick tubule of S-form. which 

 unites this bowl with the ampulla." This" stage of the development corresponds with 

 the S-shaped stage of other authors. Such early fusion of the anlagen of uriniferous 

 tubules with collecting tubules as described by Hamburger I have not observed. 

 This error of observation on his part (for such I take it to be) is, I believe, accounted 

 for by the thickness of the sections which he examined (15 to 20 m». In sections 

 of this thickness, it is often exceedingly ditficult to state whether or not renal 

 vesicles or tubular anlagen are merely "in contact with the collecting tubules or 

 continuous with them, unless the parts are most favorably sectioned, a point to which 

 I have previously called attention. That the depression on the outer side of the renal 

 vesicle and especially the clrft which opens into it is not primarily formed liy an 

 infolding of the wall was brought out in describing its formation ; the solid cord of 

 cells uniting the ampulla with the renal vesicle, as described by Hamburger I have not 

 observed. The upper portion of the renal vesicle retains a lumen as it elongates 

 toward the collecting tubule and this becomes continuous with that of the collecting 

 tubule at the time when fusion between these structures takes place. 



Authors wlio regard the uriniferous tubules as developed directly 

 from the collecting tubules are quite unanimous in their accounts of the 

 formation of this S-shaped stage of the uriniferous tubules, stating that 

 the end branches of the uriniferous tubules, or buds from these, grow for 

 a short distance toward the pelvis of the kidney and then again toward 

 the periphery, the lobule or bud thus becoming flexed, presenting first a 

 concavity, then a convexity toward the collecting tubule. I have pre- 

 viously quoted Haycraft, Gerhardt, and Stoerk as concerns this point. 

 Minot considered the capsule as playing an important role in the forma- 

 tion of the tubular anlagen. He states : " The capsule seems to prevent 

 the further elongation of the branch in its line of growth, and to force 

 the end of the branch to curl over, thus by simple mechanical condition 

 causing the formation of the anlage of the Malpighian corpuscle." Ger- 

 hardt also states that the capsule offers a mechanical obstacle to the 

 further growth of the straight tubules and thus gives the first impulse to 

 the coil formation. Assuming for the moment that the uriniferous 

 tubules are developed by a growth and budding of the collecting tubules, 

 it must be evident that other factors than the one found in the resist- 

 ance offered by the capsule to the further elongation of the branches of 

 the collecting tubules, play a part in causing these branches to curl 



