542 CKESSWELL SlIEAliEK AND DOROTHY JORDAN LLOYD. 
On a Comparison of the above Experiments. 
We have made many experiments, using both the methods 
described above on eggs from the same sea-urchin, to compare 
tlieir relative efficiency for E. esculentus at Plymouth. We 
have always obtained a higher proportion of blastulae b}' the 
use of tannic acid and ammonia, than by the use of hyper- 
tonic sea-water. 'I’able XII gives two typical examples, one 
chosen to illustrate the comparative effects on a good batch 
of eggs, the other on a poor batch. 
Table XII. 
Lot I. 
(1) 3 c.c. N/10 butyric acid -)- 50 c.c. 60°/o ))lastula> 
sea-water for 15 min. 
‘2 c.c. N/10 N aOH 50 c.c. sea-water 
for 6 mill. 
8 c.c. 2'5 M NaCl -f 50 c.c. sea- 
water for 45 mill. 
(2) 10 c.c. sea-wates- -f 40 c.c. sugar -f 80 ° blastulai 
1’4 c.c. M/(50 tannic acid for 6 min. 10°/o eggs 
1 ‘5 c.c. N/lO ammonia added for! lir. showing no 
change 
Lot II. 
Very few 
attempts at 
cleavage. 
Very irre- 
gular. 
40°/o regular 
blastulai 
Rest of eggs 
showing no 
change. 
By the use of butyric acid and hypertonic sea-water 
100 per cent, of the eggs are made to undergo some 
change, but the cultures always show much cytolysis and 
irregular cleavage. 'The blastulas obtained by this method 
are healthy, they swim up to the top of the containing vessel 
ill about 18 hours, and their moi’tality in the early stages is 
very low. With tannin and ammonia a higher percentage of 
normally shaped blastulie is obtained, frequently 80 per cent. 
The eggs which do not give rise to blastulae often do not 
show any change, and compared with the former method 
cytolysis is much less. The blastulae, however, do not appear 
healthy, many never swim up to the top of the culture-vessel, 
and even at the four-armed pluteus stage may remain near 
the bottom of the jar. Their mortality for the first few days 
