1895.] Embryology. 287 
general mixture of nucleated and non-nucleated fragments that are to 
be found when the eggs are shaken in a test tube. 
Boveri also observed that the dwarf larve had small nuclei, coming 
as he supposed from the male nucleus only, not from two fused nuclei 
as in ordinary fertilization. This reason is also fallacious since Seeli- 
ger finds a great deal of variation in the size of the nuclei in the nor- 
mal bastards from whole eggs. The small nuclei may come, then, 
from eggs with nuclei and do not give any evidence as to the absence 
of a nucleus in the egg fragment. 
Again the bastards from the whole eggs vary much in size. In 
shaken eggs, however, Seeliger finds dwarf larve much more numerous 
than in the case of whole or unshaken eggs 
He concludes that though the fertilization of non-nucleated egg 
fragments may not be impossible, it is probable that the dwarf larve 
obtained by Boveri were merely the results of fertilization of broken 
eggs or egg fragments still retaining their nuclei. 
Double Monsters.—To the same number of Roux’s new periodi- 
cal, Professor O. Schultze, of Würzburg, contributes some interesting 
results that he obtained by keeping frog’s eggs in a forced position. 
The eggs of Rana fusca were fastened to glass slides and then fertilized 
and fixed between slides so that they could not revolve when turned 
upside down. 
They were allowed to develop right side up till divided into two 
cells and then inverted and kept upside down till towards the begin- 
ning of gastrulation. 
A detailed account of the methods and of the results of individual 
experiments is given. 
It appears that a considerable number of the eggs thus exposed to 
the disturbing effects of gravitation developed into double monsters of 
various characters as shown in the two plates. Some developed two 
heads and two sets of gills on each 
The formation of these double individuals in place of the normal 
single one, isin some way due to the rearrangement of the substance 
of the cells when inverted and acted upon by gravity, so that the heavier 
part is drawn down and the lighter rises, as may be readily seen since 
it is dark colored. There is thus a modification of the egg substance 
that acts like a partial division of the egg and allows each of the two 
cells to develop somewhat as if isolated. 
In a discussion of the general question of the formation of double 
monsters in nature, the author rejects the idea that abnormal or mul- 
