AETIFICIAL PARTHEXOGENESIS IN ECHINUS ESCULENTUS. 539 
and since from the consideration of nearly allied organic 
acids it seems highly unlikely that tannic acid would even 
have the ca.rhoxyl group completely dissociated in the 
presence of such a weak base as ammonia, we have preferred 
to call the same strength of tannic acid M/60. 
In his earlier experiments Delage added the eggs to a 
mixture of sea-water, sugar and tannic acid, leaving them for 
six minutes and then adding the ammonia, and after an hour 
transferring to normal sea- water. In his later experiments 
he added the ammonia before the eggs, merely placing these 
for an hour in a mixture of sugar, sea-water, tannic acid and 
ammonia. At Plymouth, with E. esculentus we have 
failed to get any results with this later method, and all our 
blastulm have been raised by the earlier one. Table VIII 
gives a comparison of the results obtained by using the two 
methods on eggs from the same sea-urchin. 
Table VIII. 
(1) Eggs were placed in — 
(a) 1.5 c.c. sea-water 35 c.c. 1'13 M sugar solution -|- 1’4 c.c. 
M/60 tannic acid, for 6 min. 
(b) 1'5 c.c. N/10 ammonia were added to (a). 
Eggs transferred to normal sea-water after 
45 min. ....... 5°/g hlastulse. 
Ditto, after 60 min 50“/o hlastulse. 
Ditto, after 75 min 30°/^ hlastulse, hut 
rather irregular. 
(2) Eggs were placed in : 
15 c.c. sea-water 35 c.c. 1’13 M sugar solution -|- 1‘4 
M/60 tannic acid + 1’5 c.c. N/10 ammonia. 
Eggs transferred to normal sea -water 
after 45 min. ..... 
Ditto, after 60 min 
Ditto, after 75 min 
Very few attempts 
at cleavage. No 
hlastulse. 
The proportion of sea-water to 1'13 M cane-sugar solution,, 
which is best for E. esculentus at Plymouth is 10 c.c. of the 
former to 40 of the latter. This is the strength which we 
have used in all our later experiments, though we have also 
VOL. 58, PART 3. — NEW SERIES. 36 
