1619 
the reduction of the yolk-entoderm at the anti-embryonic pole is 
continued and is followed by that of the trophoblastcells, the latter 
losing for the greater part their respiratory and nutritive function 
and the scheme of the Sauropsidan egg is realised. Even in Rodents 
there is already an indication of this reduction of trophoblast cells 
at the anti-embryonic pole *). 
EXPLANATION OF THE PLATE. 
Common abbreviations. 
A. anal aperture. Am. amnion cavity. Da. intestine. Dz. umbilical vesicle resp. 
yolksack. Emb. embryonic area. Ex. exocoeloma. Lb. liver-outgrowth. Pr proam- 
nion-area. SM. segmented body-mesoderm (somatic mesoderm). Som. somatopleura. 
Spl. splanchnopleura. Zr. trophoblast. Vm. ventral mesoderm. 
Fig. 1. Diagrammatic median section through an amphibian larva with large 
yolksack. 
Fig. 2. Hypothetic transitional form between a yolkladen amphibian larve and 
the germbladder of viviparous Protamniota (median section). 
Fig. 3. Diagrammatic median section through a germbladder of a Primate with 
ectoplacental proliferations on all sides. 
In all the figures ectoderm is shown in black while mesoderm is dotted and 
entoderm hatched. 
Chemistry. — “Chemical actions in the subsoil of the dunes.” 
By Dr. J. Versrurs, M. E. Communicated by Prof. J. BorsEKenN. 
(Communicated in the meeting of March 25, 1915). 
In the dunes and the sub-soil thereof water containing the principal 
ions of sea-water is as,a rule found at a slight depth but in quite 
a different proportion, as the ions Ca and HCO, are very predomi- 
nant therein. 
Still, the concentration of the Ca-ions, which in proportion to the 
other ions occur in very large quantities, is smaller therein than in 
sea-water. At a greater deptl water is generally found in which 
the ions occur in about the same concentration and the same mutual . 
proportion as in sea-water. 
The water of the first class will in future be called the normal 
fresh water, the other the normal salt water. 
As chief ions may be mentioned 
Na, Mg, Ca, Cl, HCO, and SO, 
In the normal fresh water, the concentration of all the ions is 
1) See Srrexka, Le. H.I, 1883, Fig. 21, 24 and 25, T. II, and H. Ill, 1884, 
Fig. 9, T. XI, Fig. 13, T. XIII, Fig. 30, T. XIV and Fig. 44, T. XV. 
104 
Proceedings Royal Acad. Amsterdam. Vol. XVIII. 
