Hawaiian Marine Gastropods — OSTERGAARD 
A month later in the season another type 
of cleavage was observed in which the first 
was unequal and the second resulted in an 
embryo with three blastomeres, only the 
smaller blastomere of the first division hav- 
ing divided (Fig. 21 g, h, i) . 
The total period required for incubation 
was not recorded. The free-swimming larva 
was provided with a coiled shell and a large, 
rounded operculum (Fig. 21;', k, /). The free- 
swimming veliger larvae were kept 21 days 
in a large glass container in the laboratory. 
During this period no indication of meta- 
morphosis into the adult condition was dis- 
cernible; only a slight growth of the shell 
could be detected. 
After several days of incubation the hya- 
line envelopes within the filaments could be 
seen to contain a whirling mass of embryos 
in various stages of development, as well as 
zygotes in early cleavage stages. The obvious 
effect of this action seemed to result in the 
survival of the stronger and more advanced 
embryos over the weaker and retarded indi- 
viduals, which were knocked to pieces and 
consumed by the stronger. Thus, a form of 
cannibalism existed (Fig. 2lb) . 
Inasmuch as this mollusk is of quite com- 
mon occurrence inshore during the cooler 
season of the year and is a very prolific egg 
layer, its spawning habit could be observed 
in the laboratory, where several of the ani- 
mals were kept in a trough with running 
water in which a number of coral rocks were 
placed which bore algae and other marine 
organisms. 
When the animal deposited its filament, 
it mounted the rough surface of a coral rock 
and placed the right side of its head against 
the surface of the rock, bringing the adhesive 
filament into contact with it. The filament 
passed along the genital groove between the 
parapodial lobes on to the right side of the 
head. 
As the filament was extruded, the animal 
turned its head from side to side in a desul- 
99 
tory fashion with the result that successive 
loops formed an irregular, tangled, thread 
bundle adhering to the rock. One such fila- 
ment was found to have a length of 5.25 
meters when it was unraveled. It contained 
an estimated number of ova reaching the 
high figure of 742,720. 
Freshly deposited filaments were pale yel- 
low, but as the embryos developed the fila- 
ments became quite brown. Under favorable 
conditions of development, the free-swimming 
young were seen to escape simultaneously in 
great swarms, the egg filament being literally 
torn to bits. 
Tethys (= Aplysia) bipes (Pease) 
Fig. 22 
Like the preceding species, this large form 
occurred commonly under loose stones along 
0 1 mm. 
Fig. 22. Tethys (= Aplysia) bipes (Pease). 
a, Egg filament; b, section of filament magnified 
to show egg envelopes; c—e, jhell of free-swimming 
veliger showing operculum and otoliths. 
