332 s. HATTA : 



In ail tlie segments above referred to, tlie lateral plate of the 

 niesoblast shows the same condition as in the foregoing stages, but 

 has become more distinct from the Anlage of the pronephros. 



In the present staye of development, then, the Anlage of the 

 pronephros, is cat oß' from the myotome in more than 10 segments, 

 and the canalization has advanced in the anterior section of the 

 system, to a state just ready to put the Anlayen in the succeeding 

 somites in communication ivith one another, although the inter- 

 somitic connecting dtict in the posterior part remavns still solid. 



Figs. 51-Ô8 were drawn fron] a series of sections through 

 one of the older embryos in this stage. The intei'nal structures are 

 developed much more than in the embryo just described. The 

 cells forming the visceral layer of the myotome have been differen- 

 tiated into the muscle-plates, while the parietal layer is composed 

 of cubical cells. The Anlagen of the pronephros have acquired, 

 in most cases, a tubular structure and have grown dorsally, being- 

 folded out from the body-cavity ; I will accordingly call them the 

 pronephric tubules. 



On the right side of iig. 51, the foremost tubule ipt.l) is 

 visible, which no longer contains the internal cavity but is 

 converted into a solid mass of cells occupying the space beneath 

 the fourth myotome. This consolidation is not due to retrogres- 

 sive changes, but is effected by very active cell-multiplication 

 which takes place within the tissue. The cross-section of the 

 collecting duct seen on the left side of tig. 02 [cd.) which re- 

 presents the third section behind the last, is likewise solid. The 

 tubule on the right side of this figure {])t.2) and that on the 

 left side of tlie third section ])Osterior to it (Iig. 03, pl.'^) are 

 respectively the second tubule of the right and left side found 



