1895.] | Embryology. 769 
ing as it does the wonderful provision made by host plants to entertain 
and preserve the parasites that infest them —F. L. Harvey, Orono, 
Maine. 
EMBRYOLOGY. 
Half Embryos versus Whole Embryos.—In a brief contri- 
bution to the Anatomische Anzeiger Dr. T. H. Morgan makes an im- 
portant advance toward the comprehension of the much vexed question 
as to what may arise from part of an egg, a part or a whole embryo. 
Roux claimed that when one of the first two cells of a cleaving frog’s 
egg was killed by a hot needle, the other cell formed oniy half an 
embryo. Hertwig, however, in repeating these experiments obtained 
whole embryos of small size. Then Born showed that when a frog’s 
egg is fixed upside down, the contents rotate and become differently 
arranged. Finally O. Schultze has shown that if the egg is fixed up- 
side down in the two-celled stage, it will form two embryos, each of half 
the normal size. 
With these facts in mind Morgan repeated the experiments of Roux 
and Hertwig to see if the contradictory results might not be due to 
their having overlooked an important factor, namely, the position of 
the cells. | 
The results obtained are that when most of the 155 eggs were fixed 
upside down, six half embryos and two whole embryos were reared, 
eight in all. Of these, the six half embryos came from the few eggs 
that were fixed in the normal position, that is, with the black part of 
the egg uppermost. The two perfect, but half sized embryos, came from 
the large number of eggs fixed upside down, or with the white side 
uppermost. 
In another set of experiments subsequently undertaken, five half 
embryos were formed from 92 eggs kept in the normal position. In 
another case from 125 eggs fixed upside down seven whole embryos 
and three half embryos were obtained. 
It seems that in all the eggs tried, half embryos resulted when the 
egg was fixed in the normal position and one of the first two cells killed. 
On the other hand, in most cases tried, small whole embryos were 
1 Edited by E. A. Andrews, Baltimore, Md., to whom abstracts, reviews and 
preliminary notes may be sent. | 
