176 



B. V. HALL AND L. E. ROTH 



11. Leblond, C. p., J. Aiuit. n, 149-152 (1943). 



12. Leblond, C. P. and Gross, J., Emhcriiwlogy 43, 306-324 



(1948). 



13. Martindale, F. M., Anat. Rec. 79, 373-393 (1941). 



14. Monroe, B. G., Anat. Rec. 116, 345-362 (1953). 



15. NosEDA, J., Z.mikroskop. anat. Forscli. 60, 192-204(1954). 



16. Stoll, R. and Blanquet, P., Ann. Endocrinol. 13, 569- 



577 (1952). 



17. Stoll, R., Blanquet, P., Maraud, R., and Capot, L., 



C.R. Ass. Anat. XL" reunion. 785 (1953). 



18. Stoll, R., Maraud, R., Blanquet, P., Mounier, J., 



and Meyniel, G., Ann. Endocrinol. 17, 15-32 (1956). 



19. Tlxier-Vidal, a., Compt. rend. soc. biol. 149, 1377-1379 



(1955). 



20. Trunnel, J. B. and Wade, F. T., /. Clin. Endocr. 



Metab. 15, 107-117 (1955). 



21. Venzke, W. G., Am. J. Vet. Research 10, 272-2SI (1949). 



22. ViDAL, A., Ann. Endocrinol. 14, 444-449 (1953). 



23. Walthard, B., Bull. Scliwelz. Akad. Med. Wiss. (\955). 



24. Weber, G., Zampl G., and Ignesti, V., Arch, de Vecchi 



11, 297-308. (1954). 



25. Wolff, E. and Stoll, R., Compt. rend. soc. biol. 126, 



1215-1217 (1937). 



26. Wollmann, S. H. and Zwilling, E., Endocrinology 52, 



526-535(1953). 



Preliminary Studies on the Development an(d Differentiation of Cells 



and Structures of the Renal Corpuscle 



B. V. Hall and L. E. Roth 



Department of Zoology, University of Illinois, Urbana, and Division of Biology and Medicine, 



Argonne National Laboratories, Lemon t. III. 



Soon after Bowman published his classical descrip- 

 tion of the Malpighian corpuscle, Gerlach ( 1 ) de- 

 scribed the glomerular capillaries as lying between 

 an invaginated double layer of cells extending from 

 the inner wall of the capsule, as the intestine lies 

 within the double layered peritoneum extending 

 from the abdominal wall. Zimmermann (11) relied 

 heavily on Gerlach's concept in developing his much 

 disputed hypothesis of a glomerular "mesangium". 

 More recently others have employed Gerlach's idea 

 as a basis for a modified mesangial theory. In the 

 modified theory (7), it is supposed that a special 

 limited space, termed in a specific sense "intercapil- 

 lary space"', lies between the limbs of hypothetical 

 capillary loops. Both mesangial cells and intercapil- 

 lary space are imagined to be separated from capsu- 

 lar space by invaginated, two layered extensions of 

 the basement membrane and cells of Bowman's 

 capsule. 



Hall (3) has obtained many convincing photo- 

 graphs which afford no evidence that the glomerulus 

 is formed of simple capillary loops, as Vimtrup 

 (10) thought. If glomerular capillaries are not ar- 

 ranged as simple loops, then the whole theory that the 

 Malpighian body is formed by invagination of capil- 

 lary loops into a blind, terminal vesicle of a renal 

 tubule must be held questionable. In this respect, it 

 is important to note that the able embryologist 

 Huber (6) stated nearly fifty years ago, "the renal 

 corpuscle consists of a double-walled capsule, the 

 glomerular capsule, usually spoken of as the in- 

 vaginated end of the renal tubule, though it is not 

 developed by invagination". Huber (5) agreed fully 

 with Herring's (4) earlier conclusion that glomerular 

 differentiation takes place largely by "proliferation" 

 and "readjustments" of its cells. 



To obtain a clearer understanding of the nature 



of the cells and structures of the mature glomerulus 

 and of the embryonic processes involved in their 

 formation, we began some time ago to investigate 

 developmental stages of the Malpighian body by 

 examination of thin sections under the electron 

 microscope. 



Immediately after decapitating 1-5-day-old rats, 

 small blocks of tissue, about I mm on edge, contain- 

 ing immature glomeruli were removed from cortical 

 regions of their kidneys. The blocks were fixed in 

 1 '^o buffered OsOj solution, as described by Palade 

 (8). Washed and alcohol-dehydrated tissues were 

 embedded in a 19:1 butyl-methyl methracrylate 

 mixture. The sections were cut with glass knives on a 

 modified Minot International microtome at ^!.,^, and 

 1/40 /'. Before viewing them in a RCA-EMU-2 

 electron microscope, the sections were mounted on 

 grids with formvar membranes and immersed in 

 toluene for several minutes to remove the plastic 

 in order to increase image contrast. 



The earliest stages were recognizable chiefly by 

 the total pattern of all constituent cells, since indi- 

 vidual cells showed few or no specializations. The 

 cells were arranged in solid masses with two outer 

 layers arranged somewhat concentrically around a 

 central group of cells showing no discernible organi- 

 zation. In these earliest stages, cell membranes were 

 difficult to detect, especially between cells of the inner 

 cell mass. However, the external surfaces of the cells of 

 the inner mass (prospective endothelial cells) and of 

 the inner concentric layer of cells ( Bowman's visceral 

 layer, or prospective podocytes (2, 3)), where they 

 were opposed to each other, appeared to develop 

 prominent surface membranes very early. No defini- 

 tive capillary basement membrane, or lamina densa 

 (2, 3) was observed in these early stages. Only the 

 prominent, opposed surface membranes of the pro- 



