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PACIFIC SCIENCE, Vol. IV, April, 1950 
ployed by this mollusk to keep an intruder 
away made it evident that it was greatly con- 
cerned in preventing the removal of any of 
its eggs. 
When an attempt was made to push back 
the edge of the foot so as to expose the egg 
cases, the animal would at once move toward 
the disturbing object and spread out its foot 
in that direction. When the points of a pair 
of forceps were placed in front of it, near its 
head, it would assume an aggressive attitude 
and advance toward the forceps, touching 
them or pressing against them with its ten- 
tacles and proboscis in a determined manner. 
But the most striking method employed by 
the animal to frighten away an enemy con- 
sisted of raising the shell as high as possible 
and then with great suddenness bringing it 
downward and forward to its normal posi- 
tion, thereby agitating the water around it. 
These antics would be repeated many times 
when the animal was disturbed. 
Since an enemy from behind or from the 
sides could not always be seen, the mollusk 
was guided by touch, to which it was very 
responsive. When the forceps were placed 
against the posterior part of the foot, the 
animal would move back the shell, exposing 
the posterior part of it by retracting the man- 
tle lobes so the two "eyespots,” which are sc 
conspicuous in this species, became visible. 
Whether this had any significance or not 
could not be determined. The Cypraea did 
not stop at that, however, for the posterior 
end of the shell would be brought against 
the forceps in an attempt to force them 
away; and by means of the posterior canal 
of the shell, the animal was able to get a 
firm hold on the forceps and twist them 
slightly from side to side. The animal re- 
mained constantly on its eggs during the 
entire 1 1 days of incubation. 
A Cypraea helvola with eggs, which was 
obtained about the same time from a coral 
rock on the reef, employed, with equal vigor, 
the methods of defense observed in the above 
species, with the exception that it did not 
seem to use the uncovered posterior end of 
its shell in any way. This species has no 
"eyespots” on its shell. 
The animal remained on its "nest” until the 
eggs hatched and liberated the veliger larvae, 
upon which it promptly left, giving no further 
evidence of interest in its offspring. 
Family MIT RID AE 
Genus Mitra 
Mitra astricta Reeve 
Fig. 8 
On October 17, 1921, I found the spawn 
of Mitra astricta on a rock about 25 meters 
from shore near the laboratory. There were 
three adult mollusks on the coral rock con- 
taining the eggs, one of them being very close 
to the egg mass, which was freshly laid. This 
was taken as good evidence of parentage 
until later verification could be furnished. 
The egg cases, about 100 in number, were 
separately attached within a cavity of the 
rock, each one adhering firmly to the firm 
substratum of the rock by means of a tough, 
parchment- like base. The egg case was about 
2 V 2 mm. in length, club-shaped or oblong, 
and consisted of a thin, tough, fibrous capsule 
of a pale straw color. At the attached end 
this capsule was continuous, forming a stout, 
broad base by means of which it adhered to 
the rock (Fig. 8a). The albuminous fluid 
with which the capsule was filled contained 
from 100 to 150 ova (Fig. 8b). 
The zygotes were 0.14 mm. in diameter 
and the type and rate of cleavage were simi 
lar to those that had been observed in species 
of Cypraea and Conus. In many instances, 
however, the first division resulted in un- 
equal cleavage, but this might have been an 
abnormal condition. After the first division, 
in what appeared to be the normal, or usual, 
condition, the two equal-sized blastomeres 
contracted so as to produce an oval body of 
the two daughter cells. Such a contraction 
