DEVELOPMENT OF KIDNEYS AND FAT-BODIES IN THE FROG. 147 



not recapitulate its ancestral history correctly, and of which the 

 true history is far more perfectly preserved by the Urodeles. The 

 accounts of the development of the kidneys in Urodeles given by 

 Hoffmann, Fiirbringer, and others, are far too precise and consistent 

 to be put aside ; and we see no reason whatever for doubting that in 

 Urodeles the Wolffian tubules really arise as peritoneal ingrowths, 

 but it by no means follows that this must apply to the Anura as 

 well. It would be easy to give a long list of developmental details, 

 some of them of considerable importance, in which the frog differs 

 markedly from the newt. It will suffice here to mention the double 

 layered condition of the epiblast in the frog larva, and the consequent 

 modifications in the development of the nervous system and sense 

 organs, the formation of the anus by an independent proctodseal 

 invagination, and the mode of development of the Miillerian duct 

 In these, as in numerous other respects, the frog's development is 

 widely different from that of the newt, while comparison with other 

 Vertebrates shows us further that of the two the Urodele type of 

 development is the simpler and more primitive, the Anuran the more 

 specialised. 



2. The Nephrostomes of the Wolffian Body. — We propose first to 

 deal with the relations of the nephrostomes in the kidney of the 

 adult frog, and then to consider their condition and mode of develop- 

 ment in tadpoles of various ages. 



The existence of numerous ciliated funnel-like openings, or nephro- 

 stomes, on the ventral surface of the kidney in young frogs, was 

 first discovered by Spengel*, in 1875, by the examination of fresh 

 kidneys by transmitted light. 



Independently of Spengel, and almost simultaneously with him, 

 Fritz Meyerf discovered the nephrostomes in the kidneys of adult 

 frogs by staining the peritoneal surface with nitrate of silver. In 

 the kidney of an adult male frog he counted as many as 195 

 nephrostomes. 



In the following year, Spengel published a much fuller account 



* Spengel^ " Wimpertrichter in der Amphibienniere," " Centralblatt i'.d. mod. 

 Wissenschaft," 1875, No. 2. 



t Fritz Meyer, " Beitrag zur Anatomic des Urogenitalsystems der Selachier und 

 Amphibian," M Sitzungsberichte der Naturforschenden Ucsellscliai't zu Leipzig," 

 187'j, Nos. 2, .'J, J, p. 38. 



