96 Development and Shape of Uriniferous Tubules 



shown bv mv own observations on models of uriniferous tubules showing 

 much older stages of development than the oldest tubule reconstructed by 

 him. In this diagram, the Malpighian corpuscle is relatively too large, the 

 course given to the first part of the proximal convoluted portion is too reg- 

 ular; the proximal convoluted portion is relatively too short when com- 

 pared with the length given to the distal convoluted portion, but especially 

 wrong is the diagram in the presentation given of the descending limb 

 of Henle's loop. This, as given by Stoerk, shows essentially the same 

 diameter as the proximal convoluted portion (in his description he gives 

 it a similar epithelial lining), disregarding entirely that portion of the 

 descending limb of the loop which shows a flattened epithelium. 



In the diagram of Fig. 24 the loop itself of the loop of Henle is given 

 as formed by a tubule the same as that of the ascending limb, the transi- 

 tion from the thinner to the thicker portion of the limb as occurring in 

 the lowermost part of the descending limb. This is in conformity with 

 my models. In discussing this point, I have stated that this observation 

 was given with some reservation. I have, therefore, not called especial 

 attention to certain of the loops shown in the diagram A, B, and E of 

 Fig. 23, which are formed by the thinner portions of this structure. 



In conclusion, I desire to thank Julius H. Powers and Edward G. 

 Huber for assistance given me in the reconstructions, and Elton P. 

 Billings and Frederic G. Johnson for assistance rendered in making the 

 illustrations, — students of medicine in the Department of Medicine of the 

 University of Michigan. 



LITERATURE CITED.* 



Balfour, F. M. — On the Origin and History of the Urinogenital Organs of 

 "Vertebrates. Jour. Anat. and Phys., Lond., Vol. X, 1876. 



* BoKNHAUPT, Th. — Zur Entwickelung des Urogenitalsystems beim Hiihnchen. 

 Inaug. Diss., Dorpat, 1867. 



Beaux, M. — Das Urogenitalsystem der einheimischen Reptilien, entwicke- 

 lungsgeschichtlich und anatomisch bearbeitet. Arbeiten a. d. zool.- 

 zoot. Inst., Wiirzburg, Bd. IV, 187S. 



Chievitz, J. H. — Beobachtungen und Bemerkungen uber Saugethiernieren. 

 Arch. Anat. u. Phys. Supplement Band, 1897. 



CoLBERG, A. — Zur Anatomie der Niere. Centralb. med. Wissenschaft., Vol. I, 

 1863. 



DissE, J. — Ham und Geschlechtsorgane. V. Bardeleben's Handbuch der Anat- 

 omie des Menschen, Bd. VII, Erster Teil, Jena, 1902. 



V. Ebxer, V. — Kolliker's Handbuch der Gewebelehre des Menschen. Bd. Ill, 

 1 Halfte, Leipzig, 1899. 



Emery, C. — Recherches embryologiques sur le rein des mammif§res. Arch, 

 ital. Biol., Tome IV, 1883. 



* Contributions not seen in the original are marked with an asterisk. 



