82 
PACIFIC SCIENCE, Vol. IV, April, 1950 
Cypraea isabella Linnaeus 
Fig. 3 
During the night of July 21, 1921, a 
Cypraea isabella, which had been brought 
to the laboratory a few days before, deposited 
eggs. There were about 1,500 egg cases in 
three or four layers, held together by a gela- 
tinous matrix, with the egg cases radially 
arranged. This egg mass, measuring about 
24 x 30 mm., was fixed to the surface of a 
glass in which the animal was kept and was 
completely covered by the foot of the animal 
(Fig. 3 a). The egg case was somewhat cylin- 
drical in form, about 1.5 mm. long, pale 
straw color, and contained nearly 200 ova 
within its thick parchment wall (Fig. 3 b) . 
The development of the embryo and char- 
acteristics of the veliger are very similar to 
those of Cypraea carneola. The zygote, which 
is smaller than that of C. carneola, 0.11 mm., 
undergoes cleavage in the same manner, and 
shows a corresponding difference in size of 
macromeres and micromeres, as well as a 
similar relation of these to one another (Fig. 
3 c-h). The gastrula stage is formed entirely 
by epiboly, the micromeres spreading com- 
pletely around the macromeres. Owing to 
this condition no invagination is effected and 
the spherical form of the ovum is retained. 
This condition was reached after 3 days of 
incubation (Fig. 3/). In the trochophore 
stage, which followed, the larva assumed an 
elongate form and the large endodermal cells 
took on a distorted appearance. The foot 
began to develop as did the shell, which 
could be seen as a rudiment loosely surround- 
ing the posterior part of the body ( Fig. $j, k ) . 
The free-swimming stage was reached after 
11 days of incubation, when the larva ap- 
parently had developed all the characters of 
the veliger stage. Between the eyes now ap- 
peared an arch of bluish-black pigment, and 
the foot had a large, broad operculum, as in 
C. carneola ; also, as, in the latter, the entire 
shell was covered with small, shallow pits. 
Fig. 3. Cypraea isabella Linnaeus, a, Egg mass 
seen through glass and covered by foot of animal; 
h, egg capsule enlarged; c-g, cleavage stages; h, 
blastula; i, gastrula; j, k, trochophore with shell 
beginning to form: j, ventrolateral aspects, k, ven- 
tral aspect; l, m, veliger stage: l, lateral, m, an- 
terior aspects; n, free-swimming veliger; o, p, q, 
shell of free-swimming veliger showing (p) oper- 
culum. 
The outer lip of the shell was purplish- 
brown; the whole shell, which was about 
0. 1 5 mm. long, had a pale tinge of that color 
(Fig. 3 l-q). 
