1893. EXPERIMENTAL EMBRYOLOGY. 299 
of the pressure. The formation of micromeres was suppressed ; the 
sixteen-cell stage was a plate; and yet typical Plutei were formed 
when the pressure was removed. In other cases, a two-layered 
plate of sixteen cells was formed, and yet norma! Plutei resulted, 
a fact which seemed to Driesch definitely to contradict the concep- 
tion of His that there are definite germinal areas. What should have 
formed one pole of the embryo formed the two sides, and what 
should have formed the other pole of the embryo formed both poles. 
In fact, the segmentation-cells of sea-urchins are on to the sixteen- 
cell stage markedly homogeneous, for even after a very abnormal 
development normal larve may result. 
The Hertwigs have shown that when doubly-fertilised the ova of 
sea-urchins divide simultaneously into four. In such ova, which 
Driesch believed to have been doubly-fertilised, the whole rhythm of 
cell-division was double, so that the sixteen-cell stage was not a true 
sixteen-cell stage (with four micromeres) but a double eight-cell stage. 
But none of these forms developed. 
VII. MM. Pouchet and Chabry, experimenting in 1889 with the 
developing eggs of sea-urchins, found that when some of the lime- 
salts in the sea-water were replaced by potassium or sodium oxalate, 
the skeleton of the larva was incomplete or entirely absent. An 
apology for a Pluteus with food-canal and other organs, but without 
skeleton, was formed, even when nine-tenths of the lime was got rid 
of. Further reduction of the lime inhibited all development, even 
gastrulation. 
VIII. Following the researches of Pouchet and Chabry, the Hert- 
wigs, and others, Herr Curt Herbst of Ziirich has recently made an 
interesting series of experiments on the ova of sea-urchins. To 
the sea-water in which these were developing he added solutions 
of various salts, usually in the proportions of 3°8 grms. to 100 cm. of 
sea-water. Each experiment was checked by a control experiment 
in which the conditions were the same, excepting the addition of the 
salt-solutions. Fertilised ova were always used, to avoid the com- 
plications of polyspermy. The ova were those of Spherechinus 
gvanulanis, Echinus microtuberculatus, and Strongylocentrotus lividus, and in 
the three cases the results were practically the same. 
Forty-four experiments were made in which so much of the sea- 
water, ¢.g., 140 c.cm. out of 2,000 c.cm., was replaced by a 3°7 per cent. 
solution of KCl in ordinary water, which contained a considerable 
quantity of lime. So the observer had to deal with the addition of 
something new rather than with the removal of much lime. 
The formation of the calcareous needles was delayed ; when they 
appeared they were abnormal and always incomplete. The internal 
_ structure of the Pluteus was distinct, but the characteristic processes 
were small and rounded off. If there was less than 7 per cent. of the 
KCI solution the abnormality of the larve was less pronounced. 
These results are not peculiar to KCl, for experiments with 
