ß2 T. H. Buhlend, 



also tends to prove that these same tubules more closely exhibit 

 the mesonephric rather than the pronephric condition. 



Felix is not altogether satisfied with his statement that the 

 pronephric tubules are derived from the nephrotome for be saj^s: 



"Das Hauptkanälchen entwickelt sich aus einer soliden oder 

 hohlen Ausstülpung der Somatopleura (somatic mesoderm) des Ur- 

 segmentstieles, welche Ektoderm und kaudalwärts gerichtet ist; Aus- 

 nahmen 1. die Ausstülpung geht von Somato- und Splanchnopleura 

 aus (Teleostier), 2. die Ausstülpung geht scheinbar von der Somato- 

 pleura der Seitenplatte aus, weil der Ursegmentstiel nicht gegen 

 die Seitenplatte abgegrenzt ist oder später in dieselbe aufgenommen 

 wird (Myxinoiden, Batrachier)." 



If the region spoken of as nephrotome (Ursegmentstiel) is not 

 differentiated from the lateral plate mesoderm, and is not segmented, 

 there is no valid reason for applying the term nephrotome to it 

 at all. 



Without at this time pursuing the matter further I think that 

 we may distinguish pronephric tubules as those which arise from 

 the lateral plate mesoderm and mesonephric tubules as those wiiich 

 arise from the nephrotome. 



b) The evidence that the anterior pronephric 

 tubules and pronephric duct are developed from the 

 same rudiment, and that the duct is differentiated 

 as early as the anterior pronephric tubules and earlier 

 than the posterior pronephric tubules. 



The above condition has already been noticed in the preceding 

 account of the kidney development in Chrysemys. 



In Myxinoids (Price) most of the pronephric tubules are 

 bound together from the start by a solid longitudinal connection 

 (Längsstrang). 



In Lepidosteus Beard describes (1889) the pronephric rudiment 

 in the region of the 4th to the 8th or 9th body-segment as a solid 

 mass of mesoderm directed towards the ectoderm. Similarly for 

 Amia calva. 



In Selachii there is a divergence of opinion. Some authors state 

 that the rudiment of the pronephros consists of a row of successive 

 somatopleuric thickenings of the mesoderm of the ventral portion of 

 the protovertebrae (Ursegmenten). I have examined sections of the 

 Dogfish, and am quite convinced that the thickening is a continuous 

 non-metameric one, and that it arises from the lateral plate mesoderm, 



