1893.] Embryology. 395 
EMBRYOLOGY.’ 
Echinoderm Eggs.—Karl Fiedler’ endeavored to corroborate the 
work of Roux by experiments made at Naples upon the eggs of three 
species of sea urchin. At first the method used was that of Roux, 
piercing the egg with a needle. It was found necessary, however, to 
use a lancet shaped needle made by hammering out and sharpening the 
tip of a common needle. Later the method of shaking employed by 
the Hertwigs and by Boveri was, for the first time, adopted in separating 
the cleavage cells. 
The use of the needle under the microscope was attended with a 
great many difficulties, increased by the large mortality amongst the 
few individuals that could be successfully operated upon. After the 
membrane is quickly cut the cells may be individually punctured 
and destroyed. Such embryos can be kept only in large vessels with 
algee. 
By this means it was possible to pierce a cell so that some of the 
contents ran out without destroying its power of cleaving, providing 
the nucleus remained ; but in other cases where the nucleus escaped, 
even with but little protoplasm, the cell died. In the cases where 
cleavage continued the diminished cell gave rise to small progeny ; thus 
in the four cell stage two cells were much smaller than the others; in 
the sixteen cell stage two of the four polar micromeres were plainly 
smaller than the others; in the blastula one half was less convex than 
the other; but later the difference seems to have been equalized. 
When cells are separated by shaking, the remaining ones may change 
their shape, becoming more spherical where no longer in contact with 
other cells, but they retain their normal position much as if the other 
cells had not been removed. Thus when one of the first two cleavage 
cells was destroyed there resulted an eight celled stage that was half 
the normal sixteen celled stage, having half the normal number, four, 
of micromeres at one pole and the other cells likewise arranged as if 
the sixteen celled stage had been cut into two. The same was true of 
the half-twenty-eight cell stage. Such half embryos can be formed 
either by destruction of one of the first two cells or by destruction of 
two of the first four. The same result is produced by destroying any 
two of the first four cells, whether they are sister cells or first cousins. 
1This department is edited by E. A. Andrews, Johns Hopkins University. 
2Entwicklungsmechanische Studien. Festschrift fiir Nägeli, Zurich, 1891. 
