1893.] Embryology. 1097 
EMBRYOLOGY. 
Frog Eggs under Pressure.—Professor G. Born? describes some 
interesting experiments made upon cleaving eggs of the frog. The 
eggs were subjected to pressure by confinement between glass plates 
that pressed upon the jelly about the egg and flattened out the egg 
itself so that its diameters were as 2 to 3 or even, in extreme cases, as 
1 to 2. 
The eggs were put between the plates before fertilization and could 
thus be arranged carefully with reference to the relative position of the 
main axis of the egg and the surface of pressure. Glass strips between 
the glass plates kept these apart a certain distance, say 1:4 mm. 
Under these conditions cleavage takes place and the medullary folds 
may arise and even close over. 
If the eggs stand in their normal vertieal position—i. e., with the 
dark side uppermost and the horizontal plates press then thus in a 
direction parallel to the chief or vertical axis of the egg, the following 
departures from the normal cleavage take place. f 
The third cleavage is not, as normally would occur, by a horizontal 
furrow at right angles to the first and second furrows, but by two verti- 
cal furrows on either side of and parallel with the first furrow. The 
planes of the 1st, 2d and 3d cleavages are thus all at right angles to 
the pressing plates. This is true also of the 4th cleavage which is 
accomplished by two planes parallel to the 2d cleavage plane and at 
right angles to the first. 
In such eggs, kept under pressure, the blastopore and subsequently 
the medullary folds appear upon the under side of the egg; the ven- 
tral part of the embryo is upward in these compressed, fixed eggs. 
If the eggs are arranged so as to be squeezed from the sides, are 
compressed between plates parallel to the main axis of the egg, which 
stands vertically, then the following unusual cleavage phenomena are 
seen. 
The first plane being as usual vertical, is also at right angles to the 
pressing plates; the second is not vertical as normally would be the 
ease, but horizontal. The third cleavage is often expressed by two 
planes parallel to the first, while the fourth may be parallel to the sec- 
ond. . 
1 Edited by Dr. E. A. Andrews, Baltimore, Md. 
? Anatomischer Anzeiger, VIII, Aug. 5, '93, pps. 609-627. 
