1893.] Embryology. 397 
each pole as contrasted with the equator, where such a contraction 
takes place that at first one might regard the equatorial belt as a 
cleavage furrow. These changes involve the death of the egg, and are 
merely a “ morphological ” polarization produced by the passing cur- 
rent and localized by its direction irrespective of any axial or polar 
differentiation within the egg itself. 
However interesting and valuable the long series of experiments 
recorded in the two hundred pages of this memoir may be to the phy- 
. Sicist and to the biologist, they have for the embryologist of the present 
day too little direct bearing to make it worth while reviewing them at 
length. 
It should be mentioned, however, that the most diverse objects, frogs’ 
eggs, gall bladders, embryos, hearts, hydras, tritons, lizard and fish 
embryos, chick and mammal embryos, as well as inorganic substances, 
such as mercury, copper, lead, ete., exhibit visible differentiation of 
polar and equatorial areas dependent upon the direction of passing 
currents. Yet this is not true of even all organic bodies experimented 
with. 
Membranes of the Sea Urchin Egg.—Curt Herbst’ repeated 
the experiment of the Hertwigs, and used in addition to chloroform, 
clove oil, creosote, xylol, toluol and benzole. 
Eggs of the sea urchin shaken in water that had been mixed with 
small quantities of any one of these substances form an artificial egg- 
membrane just like that normally formed after the entrance of a 
sperm in fertilization. 
This membrane, the author holds, is made by the hardening of the 
preexistent hyalin outer layer of the egg. 
The subsequent separation of the membrane from the surface of the 
egg is probably due to the secretion of some jelly-like substance. The 
egg does not shrink away from the membrane at all. 
The sperm has no direct part in the formation of the membrane, 
but merely acts as a stimulus to the egg. If the membrane is 
removed from a fertilized egg (by shaking) the presence of more 
sperms does not cause the formation of a new membrane. If, however, 
some of the above substances are used, a second membrane is formed. 
Two membranes, one inside the other, may be formed from eggs having 
one membrane, or even from those having the first membrane removed. 
The cause of this membrane formation is to be sought for in the egg 
itself. 
5Biol. Centralblatt, Jan., 1893. 
