Hatching in Aquatic Invertebrates, IX and X — Davis 
379 
from an average of 1,590 to 1,770/x. No signs of 
drinking were observed at this time, and there- 
fore the obvious uptake of water must have 
been across the surface of the embryo after the 
water had permeated through the egg mem- 
brane. Thereupon the embryo squirmed and 
twisted, and the membrane broke at the anterior 
end, liberating some of the anterior appendages. 
It took approximately 1 min for the membrane 
to slip off, thus completing the hatching. At 
an average of 7 min after the break in the 
membrane occurred, the young isopods had in- 
creased to a length of 1,890/x. 
It was observed that embryos within their 
membranes, whether some time before hatching, 
or nearly ready to hatch, were able to live for 
over 24 hr in the external sea water, but they 
became weaker and weaker, and shortly there- 
after death ensued. In those ready to hatch, 
hatching was unsuccessful if they had been out 
of the brood pouch more than about an hour 
before initiation of eclosion. It is not thought 
that the sea water used was toxic, for the parents 
were living in it. Either lack of nutrients pro- 
0.4 MM 
FIG. 1. Cirolana sp. Early egg removed from the 
brood pouch. There is a large fluid -filled space between 
the developing embryo and the loosely fitting egg 
membrane. 
0.4 MM 
Fig. 2. Cirolana sp. An embryo shortly before 
hatching. There has been a great increase in size, com- 
pared to the early stage shown in Figure 1. The 
membrane is thin and tightly stretched. A fluid-filled 
space remains, however, between it and the embryo. 
