( 808 ) 



3. At the end of t lie covering of the yolk, at the closure 01 

 the blastopore, KupfFkr's vesicle is formed after the manner described 

 at length in my former paper. By Swaen and Brachkt ■) and by 

 Sumner the narrow passage connecting' this vesicle with the exterior, 

 through the closing blastopore, is regarded as representing the neuren- 

 teric canal. I do not think they are in the right here. Kupffer's vesicle 

 is a ventral formation. Dorsally it is separated from the cells of the 

 medulla by the cells of the prostomal thickening and the pavement 

 layer. An open canalis neurentericus is not found even in these forms. 

 Kupffer himself called the vesicle allantois. Hdbrbcht followed him 

 in this. In my former paper I compared the vesicle with the allan- 

 tois of amniota on physiological grounds, and I think it is a very 

 good thought of Hubrecht to take up the old name of KüPFFERand 

 compare the vesicle with the allantois on morphological grounds. 



DESCRIPTION OF FIGURES ON PLATE 1 AND 2. 

 Plate 1. 

 Figg. 1 — 4. Median sections through eggs of Muraena N°. 1 on different stages 

 of gastrulation. In fig. 3 gastrulation is finished and notogenesis is begun. In fig. 2 

 the structure of the yolk is drawn. Enlargement 40 times. Fig. 4c/, .") and 6 give 

 median sections through the developing prostomal thickening and adjoining parts, 

 seen under a higher power. 



Figg. 7 — 9. The flattening of the blastodisc at the beginning of gastrulation in 

 eggs of Muraena N°. 7. Enlargement 4') times. 



Plate 2. 

 All the figures on this plate are drawn from life as accurately as possible. 

 Fig. la — le. Covering of the yolk in an egg of Muraena N . 1. 

 Fig. 2a— 2d. Covering of the yolk and elosure of the blastopore in an egg of 

 Muraena N°. 1. By means of a fine needle one of the oil-drops is nearly severed 

 from the surface of the yolk, remaining connected with the periblast only by means 

 of a thin protoplasmatic thread. In fig. 2c this oil-drop is cut off from the surface 

 of the egg by the travelling blastodermring and is lying close against the egg- 

 capsule EK. In fig. 2(7 (closure of the blastopore) this oil-drop is no more drawn 

 in the figure. 



Fig. 3. Unusually fargoing dislocation of the hinder end of an embryo during 

 the covering of the yolk. The head end lies approximately at the former centre 

 of the blastodisc. 



Fig. 4. Compression of the yolk-sphere by the growing blastodermring in an 

 egg of Muraena N'. 4. The oil-drops only temporarily changed their relative dis- 

 tances a little. 



OD = oildrop. 

 pv = prostomal thickening 

 per = periblast. 

 Bl = blastoderm. 

 D = pavement layer 

 e = entoderm 

 Leiden t 17 January 1907. 

 2) Archives de Biologie T. 20. 1904. page 601. 



