The Post-Metamorphic Development of the Kidney.

1. The principal changes are in the method of attachment of malpighian unit to archinephric duct.

2. In the anterior region of the kidney there are few functional units attached to the straight tubules. (Text-fig. 1, A, C, F.)3. In the middle region of the kidney there are many functional units attached to the straight tubules. (Text-fig. 1, B, D, G.)4. Additional units are produced, after the end of the first year, only in the posterior region of the kidney.

5. There are no straight tubules in this newly formed posterior region so that the units become attached to outgrowths from the archinephric duct. (Text-fig. 1, E, H.)6. These outgrowths, termed collecting-trunks, branch and anastomose.

7. Accessory peritoneal funnels are formed from blastema lying in that part of the kidney which adjoins the gonad. (Text-fig. 2, C.)

8. These funnels are furnished with longer tails than those previously produced. (Text-fig. 2, D.)

9. The tails are in close association with renal arterioles which subsequently pass to excretory units.

10. It is suggested that the arterial supply of the ‘tail’ may purify the coelomic fluid which the funnels return to the renal venules.

The Development of the Vasa Efferentia.

11. The origin of our present conception of the formation of the vasa efferentia is traced to Gaupp's adoption of Beissner's compromise between the views of Hoffman and Spengel. (Pp. 454 to 458.)

12. The gonadic ridge is primitively connected to the region of the developing kidney by a sheet of kidney blastema. (Textfig.3, A.)

13. This sheet breaks up into (a) a series of rudimentary vasa efferentia; (b) an anterior prolongation connecting the anterior end of the gonad to the anterior end of the kidney. (Text-fig. 3, B, C.)

14. The rudimentary vasa efferentia ends in a mass of blastema lying along the edge of the kidney.

15. This mass, from which Bidder's canal subsequently develops, is itself connected to the abortive unit which terminates the straight tubules. (Figs. 9a and b, Pl. 21, Fig. 4, Pl. 20.)

16. The anterior prolongation ends in a mass of kidney tubules at the anterior end of the kidney. (Fig. 8, Pl. 21.)

17. It is suggested that these anterior units are without functional significance.

18. The testis end of the anterior prolongation grows downwards into the testis and becomes connected to the tubules and vasa efferentia. (Text-fig. 3, D.)

19. The kidney connexions of the vasa efferentia remain unaltered but the anterior prolongation degenerates (Text-fig. 3, E.) The Development of the Seminal Vesicles.

20. In a four-legged tadpole there is a mass of mesenchyme, containing aggregations of kidney blastema, on the side of the archinephric duct between the points where this leaves the kidney and enters the rectum. (Fig. 26, Pl 23.)

21. The mesenchyme forms connective tissue and the blastema aggregations form short tubules.

22. During the third year after metamorphosis these tubules branch and coil.

23. It is emphasized that the seminal vesicle derives nothing from the archinephric duct, and suggested that it may represent the remnants of the most posterior units of the sexual kidney.

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