DEVELOPMENT OF KIDNEYS AND FAT-BODIES IN THE FROG. 155 



easy it would be for sagittal sections, such as he figures, to give false 

 impressions concerning the relations of the fat-bodies to the kidneys. 



IV. Summary of Kesults. 



Our own observations are confined to tadpoles and adults of 

 Banco tenvpomria. 



1. The head kidney and its duct are mesoblastic structures: the 



epiblast takes no share in their formation ■ but the cloacal 

 openings of the ducts are formed partly by outgrowth from 

 the gut. 



2. The head kidney is a large and complex organ during early 



larval life, but begins to degenerate in tadpoles of about 20 mm. 

 length. 



3. The first stage in the degeneration of the head kidney consists in 



great and irregular dilatation of the tubules, accompanied by 

 destruction of their epithelial lining, and apparently due to 

 blocking of the archinephric duct. 



4. The head kidney ultimately completely disappears; all three 



nephrostomes close up, and atrophy. 



5. The peritoneal opening of the oviduct is a new formation, and 



not a persistent nephrostome ; it is produced in a somewhat 

 complicated fashion. 



6. The tubules of the "Wolffian body begin to form shortly before the 



head kidney degenerates ; they develope from behind forwards, 

 and are at first segmentally arranged. 



7. The Wolffian tubules are formed from the mesoblast between the 



aorta and the archinephric ducts, and arise independently of the 

 peritoneum. 



8. Nephrostomes are formed at an early period, and open into the 



body cavity. There is reason for thinking that they at first 

 communicate with the necks of the Malpighian bodies ; but 

 they very early lose all connection with the urinary tubules, 

 and in the later larval stages, as well as in the adult, the}' 

 open directly into the renal veins. 



9. The fat-bodies are formed from the anterior ends of the genital 



ridges. 



