328 s. HATTA : 



of cross-sections through one of these eniliryos whicli lias abont 25 

 somites. The neural cord {n.) is reduced in size and in the anterior 

 part has a conspicuous canal. The myotomes which showed 

 before a pentagonal outline, in the anterior part of the body have 

 now assumed an elongated lozenge-shape^^ and is composed of an 

 outer, and an inner, layer of long cells whicli have begun to dif- 

 fentiate themselves. The inner layer (mus.) represents the median 

 and ventral rows of the pentagonal myotome mentioned on p. 320 

 and, therefore, corresponds to the visceral layer of the myotome ; 

 the outer layer {cuL) is the product of the dorsal and lateral layers 

 and constitutes the parietal layer. The pronephric Anlage is com- 

 posed of high columnar cells which are plainly distinguishable 

 from the much shorter elements of the lateral plate (Im.). The 

 component cells of the Anlage of the pronephros which we generally 

 found to be compressed in the foregoing stage (pp. 324 and 32Ö), 

 are now more or less loose, and the internal cavity of the Anlage 

 is somewhat widened, being distended by the loosening of the cells.'' 



The peritoneal cavity is, at the present stage, still repre- 

 sented merely by the boundary-line of the parietal and visceral 

 layers of the lateral plate. 



In the present stage, the foremost Anlage of the pronephros 

 is, as before, found under the hind part of the fourth myotome 

 (figs. 32-35, a.pn.l). The Anlage shows, in section, a circular 

 outline and is composed of high columnar cells arranged in a 

 radial manner. The internal cavity of it is confined no longer 

 to one section, but it is observed in three or more sections ; it 

 is most spacious in the hind part of the fourth somite (fig. 33) 

 or in that part where the cavity is visible from an early period. 



])Afew myotomes in the anterior somite'^ tend to assume this shape alrcaily in the last 

 stage (see figs. 20, 21, and 22). 



2) See the foot-note on p. ?>ld. 



