338 



s. HATTA 



a-b indicates the extent of the 

 coelomic projection. When tlie 



Wnud-L'ut 1. — Seiuidiagniniatic tigiues to 

 illustrate the siK;ces.sive jjliases of the 



evolution of the nephrotome. 

 I'roiu the right side of fig. 16. 

 from fig. •'>. 



from the right side fig. 18. 

 from the left side of the same, 

 from the left side of fig. 53. 

 from the right side of fig. 55. 

 from the left side of fig. 61. 



called the coelomic projection 

 plate of epithelial cells {G, c.p. 



Anlage ; c-d shows that of the 

 myotome is cut oft', the point 

 of the parietal layer indicated 

 by a becomes fused with the 

 point r of the visceral layer 

 (B, ac). This piece of the meso- 

 blast assumes an ellipsoidal sha2)e 

 (C). The component cells of 

 this ellipsoid are multiplied by 

 active cell-divisions, and the 

 piece almost loses its lumen and 

 gets a compact consistence {D). 

 Meanwhile the cells in the space 

 d-c remain inactive. Conse- 

 quently the piece acquires a tri- 

 angular form (E), whose upper 

 sharp angle, together with the two 

 sides enclosing this angle, gives 

 rise to the pronephric tubule. 

 The lower (median) obtuse angle 

 now begins to grow by cell- 

 mulplication {F) and produces 

 a small knob {F, c.p.), which 

 grows further and pushes in be- 

 tween the myotome and the 

 hypoblast (the upper wall of the 

 enteric canal). This cellular 

 projection is that which has been 

 It is reduced into a thin 

 ) and assumes then the form of 



