( 805 ) 



fig. 4.. 5 and 6 on plate 1). It seems probable, that at least in some 

 cases entodermcells are formed by delainination from the periblast at 

 some distance from the surface in front of the prostomal thickening 

 (fig. 5e). So here, as in many vertebrates, the entoderm is formed 

 bv delainination. At the moment of the differentiation of the pros- 

 tomal thickening (figs. 2, 4), there is still no trace of the invagination 

 of the mesodermcells, only a thickening of the mass of cells lying 

 just overhead of the cells of the prostomal thickening. Immediately 

 afterwards however a distinct differentiation of the mesoderm becomes 

 visible. At that stage the notogenesis begins and the gastrulation 

 process js finished. The prostomal thickening is the ventral lip of 

 the "blastopore reel" of the Amphibian egg. For the developmental 

 processes following on this stage I can contain myself with referring 

 to my former paper. That here only a small, not very prominent 

 tail-knob is formed and no far-reaching projecting tail-folds appear, 

 as in the selachean embryo, is caused by the relation of the pave- 

 ment-layer to the blastoderm and the periblast, which influence the 

 development of teleostean egg ("développement massif" of Henneguy). 



2. To determine the direction of growth of the blastodermring 

 during the covering of the yolk, I used in my former paper the 

 oil-drops in the yolk of the muraenoid eggs as a point of orientation, 

 on the contention that these oildrops maintain (in the muraenoid 

 egg) a constant position in the yolk. On this basis I constructed a 

 scheme of the mode of growth of the blastoderm in the yolk. x ) 

 Both Sumner and Kopsch rejected this contention and the scheme, 

 Sumner because of the fact, that by inverting the egg of Fundulus 

 heleroclitus in a compress, the oil-drops may be caused to rise 

 through the yolk and assume a position antipodal to their original 

 one, which shows, that here the oil-drop may not be regarded 

 as a constant point of orientation in the egg. In this Sumner is 

 perfectly right. Not only in Fundulus, but in several marine pelagic 

 eggs too the oil-drops may be seen travelling through the yolk by 

 converting the egg or bringing the young larva (in some species) 

 in an abnormal position. In the muraenoid egg however the case 

 is entirely different. Here the structure of the periblast and of the 



not judge, but I will only mention here, that the figures, drawn by the author, are 

 taken of much too late stages of development, to be convincing. And after all, 

 where the blastodermcells are so much alike, as is the case in most teleostean 

 eggs, one positive result in a favourable case as is offered in the muraenoid egg, 

 is more convincing than several negative results in less favourable eggs. 



l ) 1. c. page 142. 



