Oo6 CRESSWELL SHEARER AND DOROTHY JOUDAN LLOYD. 
After treatmeut with sea-water of raised alkalinity the 
eggs are put into hypertonic sea-water. For Echinus 
esculeutus iu general 8 c.c. 2‘5 M NaCl -(- 50 c.c. sea- 
water for 'TO-l hour gives the best results. These numbers 
are the same as those given by Loeb (17) as most satisfactory 
for the sea-urchins of the Californian coast. Both the 
strength of the hypertonic solution and the time during 
which the eggs are allowed to remain iu it are of importance 
in bringing about parthenogenesis in many cases, but the 
experiments which we have made have convinced us that the 
condition of the eggs is the most important factor in deter- 
mining whether parthenogenesis can, or cannot, be induced by 
chemical means. Frequently eggs are found to separate 
freely from the ovaries when the latter are shaken in water, 
and to appear ripe under the microscope, being spherical and 
having no visible nuclei. These may, however, fail to develop 
parthenogenetically, although varying strengths of hypertonic 
sea-water be used for different lengths of time. On the 
other hand, with some eggs (see Table VII below) 8 or 9 c.c. 
2'5 M NaCl + 50 c.c. sea water appeared to act equally 
well. 
In the results recorded iu Table V the strengtli of the 
hypertonic solution used has been varied ; iu Table VI the 
time during which the eggs were exposed to its action ; in 
'Table VII both time and strength are variable. In all the 
experiments the eggs had previously been treated with butyric 
acid to cause membrane-formation and then with sea-water of 
raised hydroxyl ion concentration. In each series all con- 
ditions except those of the hypertonic sea-water were constant 
for the series. 
Table V. 
Lot I. Lot II. 
(1) 4 c.c. 2'5 M NaCl -|- . Very little attempt . — 
50 c.c. sea-water at division 
for 45 min. 
( 2 ) 5 c.c. ditto ... - — .A few irregular at- 
tempts at cleavage. 
