SUMMARY. 41 



forward in two baads — one on each side — between the ectoderm 

 and endoderm (PL V, figs. 36 a and b,mb.). They seem to 

 arrange themselves on the strands, connecting the ectodermal 

 and endodermal reticulum, and they constitute the mesoblastic 

 bands. A series of vacuoles are formed in these bands, around 

 which the nuclei arrange themselves in rows, thus giving rise 

 to the mesoblastic somites. 



The further development I shall describe in the next 

 chapter. 



Summary and General Conclusions. 



The Segmentation is apparently complete, the ovum appearing 

 to divide into ectoderm and endoderm cells. 



The so-called endoderm cells are at first without a distinct 

 nucleus, they do not get a nucleus until just before the gastrula 

 stage. 



All the cells of the ovum, ectodermal as well as endodermal, 

 are connected together by a fine protoplasmic reticulum, which 

 is placed, as are also the cells, immediately beneath the egg 

 membrane, and therefore around a central space. 



Each ectoderm cell consists of a central nucleus ai'ound which 

 is a close protoplasmic spongework, which, at the outer parts 

 of the so-called cell, becomes of a gradually looser nature until 

 it runs into the spongework of the surrounding cells. 



Each endoderm mass consists of a central denser spongework 

 which gradually becomes looser towards the periphery of the 

 mass until it is continued into a fine reticulum. The endoderm 

 masses are far apart from each other and are connected by 

 this reticulum. 



The continuity of the various cells of the segmenting ovum 

 is primary and not secondary, i. e. in the cleavage the segments 

 do not completely separate from one another. But are we 

 justified in speaking of cells at all in this case? The fully 

 segmented ovum is a syncytium, and there are not 

 and have not been at any stage cell limits. I think 

 the cleavage should be rather desci'ibed not as segmentation, 



