360 



s. H ATTA : 



(nephrostomal) portion of the two following pairs is directed 

 backwards. The nephrostomes retain their first position {B). 



Now the secondary curvatnres take 

 place {0). The nephrostomal part 

 of the foremost pair is crooked just 

 like that of the two hind pairs in 

 B ; the middle tubule is bent for- 

 wards like the foremost tubule. 

 The hindmost tubule makes a 

 small forward curvature and a 

 large backward bending. In the 

 next stage, D, the foremost and 

 the middle undergo no marked 

 change, but the secondary curva- 

 tures of the hindmost tubule are 

 much more strongly expressed. In 

 E the foremost receives a second- 

 ary curvature directed backwards 

 at the middle part ; the middle 

 acquires a curvature in opposite 

 direction; the hind tubule undergoes 

 no marked change except in the 

 increased de2;ree of the ori2;inal 

 curvatures. It seems that the 

 subsequent bondings always take 

 place in the curved portion until there arises a system of com- 

 plexly convoluted tubules filling up the chest cavity. 



As has been said, throughout these phases the positions of 

 the nephrostomes are not markedly changed, retaining the same 

 condition for a considerable period. The bendings of the tubules 



Wood-cut 2. — Di ashrams 

 sliowing the convolutions 



of the tubules: in later stages, 

 t. pronephric tulMiles. 



Sil. segmental dnct. 



