I 
AETIFICIAL PARTHENOGENESIS IN ECHINUS ESCULENTUS. 533 
III. Loeb’s Improved Method (figs. 5-9^ and 12, 14, 15 
and 16). 
The method elaborated by Loeb (17) for bringing about 
artificial parthenogenesis in the eggs of sea-urchins consists 
in first treating the unfertilised eggs with sea-water to which 
small quantities of butyric or any other fatty acid has been 
added, and afterwards with hypertonic sea-water. Owing’ to 
the fact that the sea-water at Plymouth has a lower con- 
centration of OH ions than that of the water of the American 
coast, it is necessary, in order to obtain successful results by 
this method at Plymouth, to transfer the eggs from the butyric 
acid solution to sea-water in which the OH ion concentration 
has been raised by the addition of small quantities of NaOH.. 
After lying in this hyper-alkaline sea-water for a short time 
the eggs are changed to the hypertonic solution, and on being- 
returned to normal sea-water segmentation takes place. 
We have tried various strengths of butyric acid for longer 
and shorter times, as shown in the following table. The best 
membrane formation was bi’ought about by using a mixture 
of 3 c.c. X/10 butyric acid and 50 c.c. of sea-water for P5 
minutes. 
Table I. 
Lot I. Lot II. 
(1) 1 C.C. N/10 butyric acid -j- 
50 c.c. sea-water for I’o 
mill. ..... 
No memln-anes . 5°L membranes.. 
(2) Ditto, 2'0 mill. 
A few 
(3) Ditto, 2 5 min. 
A few 
(4) 2 c.c. ditto, 15 min. 
60°/o poor .. 
• iO-lo 
(5) Ditto, 2'0 min. 
O 
o 
o 
00 
. 
(b) Ditto, 2'5 min. 
60°, 0 „ .. 
— 
(7) 3 c.c. ditto, I'o min. 
70°/o good .. 
. 95°/o good .. 
(8) Ditto, 2'0 min. 
70°/o poor .. 
. 20°/, „ ,. 
(9) Ditto, 2'3 min. 
70°/o „ .. 
. 25°/, ., „ 
(10) Ditto, 3'0 min. 
— 
• 15°/, „ „ 
Besides using membrane-formation as 
a criterion for the 
time and strength of the buty 
ric acid, Ave 
also made experi- 
ments in which, after treating 
with butyric acid, the eggs are- 
