364 s. H ATT A : 



ranged a« in the Anlagen in the anterior region. Fig. 89 represents 

 the section through the twenty-eighth somite in the series of sections 

 shown in iigs. 77-86 ; it is the hindmost section in this series of 

 sections, in which the cells just spoken of are detected ; there are 

 found a few cells {((..sd.) of this kind which show no definite struc- 

 ture, hut are scattered. In the next anterior section (fig. 88) the 

 cells are arranged more or less radially. In the sections lying 

 further anteriorly to this a perfect tuhe is formed as seen in fig. 87 

 (•sï/.) which shows the frontal section through the seventeenth to 

 twenty-third somites in the same series as the above two figures.^^ 

 In what somite this nKxlified mode of the formation of the duct 

 begins I can not tell with exactness, but it is certain that the duct 

 arises by the differentiation of the nephrotomic cells in situ more 

 than 10 segments back of the hindmost pronepliric tubule. I have 

 considered it possible that tliese cells {a.-sd.) might be epiblastic in 

 origin, Ijut I can not find that the cells composing the epiblast over 

 this cell-group show any sign of mutiplication ; while on the 

 other hand, the cells on the dorsal edge of the lateral plate 

 (which corresponds to the nephrotome in the anterior part) are 

 very active. I see, therefore, no escape from the conclusion that 

 these cells are mesoblastic in origin. 



Also in the anterior part (jf the body, the epiblast consists 

 throughout these phases of development always of a single 

 layer of cubical cells and shows a sharp contour against the 

 structure inside it, being, in most cases, intervened by a space. 

 Naturally, mitotic figures are observed at several points, but the 

 products of these cell-divisions contribute only to the extension 

 of the epiblast itself, as may be inferred from the direction of 



1) By the l)ending ul" tlic body-axis, some sections in a series of cross-sections arc iin- 

 avoidablv cut throutrh frontallv. 



