610 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
the effect produced by the destruction of one of the first blastomeres in 
Siredon pisciformis, in the only case in which he obtained any result, a 
half-embryo of the right side was produced. 
Herr H. Driesch* finds that it is easy to shake the fertilized ova of 
sea-urchins so as to liberate the membranes. Membraneless ova placed 
under the pressure of a cover-glass, as in a former experiment by 
the same investigator, divide into 8-celled stages, in which the blastula 
consists of an annular zone of “ animal ” cells and two separated zones 
of “ vegetative ” cells. It is as if the “ animal ” cells formed the 
tropical zone, and the separated “ vegetative ” cells the polar-temperate 
zones. Yet from these there develope normal Plutei. “ It is there- 
fore proved that from a blastomere something may result quite different 
from that which would have resulted in normal development.” While 
the material of the normally “ vegetative ” half is separated into two 
distinct zones, the resultant gastrula has but one gut; therefore at 
least some of the cells which would normally have formed “ endoderm ” 
do in reality form “ ectoderm.” 
Dr. F. Braem t points out a fallacy in one of Driesch’s arguments. 
Driesch exposed developing ova of Echinus microtuberculatus to the 
pressure of a cover-glass with the result that a two-layered plate of 
eight cells on each layer represented the blastula-stage. “ What should 
have formed one pole formed the two sides, and what should have formed 
the other pole formed both poles.” Yet normal Plutei developed, 
whence Driesch concluded that the segmentation-spheres were uniform 
and might be arranged in any way without affecting the result. There- 
fore the doctrine of specific germinal areas must be corrected. But 
Braem notes the unproved assumption that the eight cells formed under 
the influence of pressure are the equivalents of the cells in the normal 
eight-cell stage. That this assumption is likely to be incorrect is shown 
in detail. Driesch’s experiment showed only that the normal form of seg- 
mentation may be greatly altered without affecting the ultimate develop- 
ment. Nor is the doctrine of His affected by the fact that one of the first 
two segmentation cells may form a complete gastrula, for this is simply a 
striking instance of regeneration, and the power of regeneration is natu- 
rally energetic in the immediate cell-descendants of a fertilized ovum. 
Heredity and the Theory of Descent. :f — Prof. C. Emery discusses 
the recent developments of Darwinism at some length. At the outset 
he explains his own position to be that of a Darwinist in the narrower 
sense ; he considers natural selection to be a highly important, but not 
the only, perhaps not even the most important factor in evolution. 
The first point taken up is that of secondary sexual characters. The 
possibility of sexual selection is granted in the case of certain birds ; 
in polygamous birds it is however a fact of observation that the females 
belong to the conqueror, and some of these birds are brightly adorned. 
The suggestion that the bright colours, &c., of the male serve as an 
indication of his strength is noticed ; it can, however, hardly account 
for the beautiful patterns and combinations of colour. With regard to 
many of these characters, as, for example, peacocks’ feathers, the pregnant 
* Anat. Anzeig., viii. (1S93) pp. 348-57 (16 figs.). 
t Biol. Centralbl., xiii. (1893) pp. 146-51. % Tom. cit., pp. 397-420. 
