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PACIFIC SCIENCE, Vol. IV, April, 1950 
The parchment- like walls of the filament 
were rather thick and the lumen was tightly 
packed with ova. The ova, as in other genera 
of this family, were enclosed in hyaline cap-* 
sules which usually contained one ovum* 
Sometimes there were two ova in a capsule, 
in which case the capsule was of an oblong 
form, instead of being globular or oval as 
were those containing only one ovum. 
The diameter of the zygote was about 0.07 
mm. and its first cleavage was unequal, as 
in Tethys grandis , resulting in one macro- 
mere and one micromere. The micromere 
divided next, equally, then the macromere, 
also equally, resulting in a stage of two 
macromeres and two micromeres. The two 
macromeres remained undivided, while the 
micromeres rapidly increased in number and 
formed a cap at the animal pole over the two 
yolk-laden macromeres at the vegetal pole 
(Fig. 25b). 
The free-swimming veliger stage was 
reached in the short period of 6 days, when 
the handsome little larvae, whose shells 
measured but 0.09 mm. in length, emerged 
from the filament. The parts of the larva 
enclosed by the shell appeared to be straw 
colored, while the velum and foot were color- 
less; the veliger lobes were rather small 
and rounded, the operculum was broad and 
rounded and extended well beyond the foot. 
Otocysts were present, but no eyes. The col- 
umellar region of the shell had a light car- 
mine tinge and the suture was of a deep 
reddish-brown. The rest was pellucid and # 
colorless (Fig. 25c, d, e). 
Family HYDATINIDAE 
Genus Hydatina 
Hydatina amplustre (Linnaeus) 
Fig. 26 
On the morning of January 4, 1921, I 
found an egg receptacle in a glass dish with 
a Hydatina amplustre ; this also served to 
Fig. 26. Hydatina amplustre (Linnaeus), a, 
Animal that laid the egg structure; b, egg struc- 
ture; c, d, free-swimming veliger: c, ventral, d, lat- 
eral aspects; e—g, shell of free-swimming veliger 
showing operculum and otoliths. 
identify several such structures that had been 
found dose to the laboratory. The receptacle 
was a broad, white ribbon, intensely folded 
and attached to the surface of the dish with 
a broad adhesion disk. The ribbon had a 
width of about 1 centimeter and contained 
within its walls masses of ova enclosed in 
hyaline capsules. Development of the embryo 
was not investigated. 
The free-swimming veliger possessed oto- 
cysts but not eyes. Two conspicuous elongate 
dark spots appeared on the ventral side of 
the foot near the tip, and an operculum was 
present on the opposite side. The clear, color- 
less veliger shell measured about 0.125 mm. 
in length (Fig. 2 6a— g). 
Hydatina physis (Linnaeus) 
Fig. 27 
On November 16, 1922, an egg structure 
