362 s. HATTA : 



The Anlage thus pronounced in each somite soon assumes a 

 characteristic oval form, being completely cut off from the myo- 

 tome to which it belongs (compare the right side of fig. 3 with the 

 right side of fig. 58 and see the description on p. 335). The mode 

 of constriction is also the same as in the case of the pronephric 

 tubules ; the indentation begins at the anterior and posterior 

 borders of the somite, and the middle portion is cut off last 

 (compare with the explanation on p. 320). 



Here also, the coelomic projection is formed in the same mode 

 and at the same point as in the case of the pronephric tubules (see 

 left side of fig. 63, r.y;.). 



Up to about this time, the Anlage shows a feature much 

 resembling that of the tubule, so that one who has not followed its 

 further history might mistake it for a pronephric tubule (compare 

 the left side of fig. 63 with figs. 67-74). But cell-mutiplication 

 which occurs almost invariably in the case of the pnmephric 

 tubules, is not observed in the Anlage of the segmental duct 

 which is soon cut off from the lateral plate (including the coelomic 

 projection) and assumes a characteristic tubular structure com- 

 posed, in cross-section, of radially arranged cells of columnar shape. 

 Its position is always on the parietal aspect of the dorsal (proxi- 

 mal) angle of the peritoneum where the coelomic projection passes 

 over into the lateral plate (see fig. 75). This separation of the 

 Anlage of the duct from the lateral plate goes on, it seems to me, 

 on tlie whole from the anterior part to the posterior, but often ir- 

 regularly ; for not infrequently, the duct in some anterior somite is 

 connected with the lateral plate, while it is already cut off com- 

 pletely in posterior somites. In fact, there are some somites in 

 which the separation is very much delayed and I have often been 

 sur})rised to find what appeared like a prone})hric tubule in a 



