114 
PACIFIC SCIENCE, Vol. IV, April, 1950 
ing a gastropod fauna similar to the one of 
Hawaii. Such faunas are found in Microne- 
sia. We may then postulate that ocean cur- 
rents from that region were the source of 
distribution of the marine gastropods of 
Hawaii. The veliger larva could be carried 
east by the North Equatorial Current, which, 
along its course, might yield parts of its 
planktonic cargo to the westward- flowing 
Japan Current to be carried by it to the Ha- 
waiian Archipelago. If this be the chief, or 
only, method of deriving our marine gastro- 
pod fauna, we must at once recognize the 
importance of a long free-swimming exist- 
ence to the successful migration over vast 
ocean barriers. 
Phylogenetic Significance of Veliger Shell 
The great dissimilarity between the veli- 
ger larva and the adult gastropod may have 
its explanation on the basis of adaptation on 
the one hand and heredity on the other. 
To structures that have developed as adaptive 
measures in the larva is applied the term ceno- 
genetic in contradistinction to the term pal- 
ingenetic, which deals with characters of an- 
cestral significance, thus throwing light upon 
the evolutionary history of the organism. 
The ciliated veliger lobes by means of 
which the larva leads its pelagic existence 
appear important to the distribution of nu- 
merous species and might therefore be classed 
as an adaptation. We can, however, conceive 
of a minute gastropod ancestor, which, like 
the wheel animalcule (Rotifera), was pro- 
vided with ciliated lobes that served both for 
locomotion and food getting before it devel- 
oped its protective shell. Concerning the 
veliger shell it will be noted that it was pres- 
ent in the opisthobranch larva as well as in 
that of the prosobranch, even in groups where 
it is entirely lacking in the adult animal. In 
addition to the veliger shell an operculum 
was found in all but two species, Conus 
hebraeus and Pleurobranchus sp. I have failed 
to see any service of the operculum to the 
veliger larva. During the active existence of 
the larva, the foot with its operculum was 
fully extended, and only when a larva sank 
to the bottom to die was the operculum seen 
to close the aperture to the shell. 
Veliger larva and shell both show a close 
approach to a bilateral symmetry, which in 
later development is lost by coil formations. 
It appears that both the veliger larva and 
the shell with the operculum have a palin- 
genetic significance in which the swimming 
apparatus, the veliger lobes, have been re- 
tained owing to their functional value, com- 
ing to overlap in time, as it were, a later 
ancestral structure, the shell. 
Supportive evidence for such a contention 
may be found in a comparison of the veliger 
shell with some of the fossil gastropods of 
the early Paleozoic era, Cambrian and Ordo- 
vician, which show simple shells of bilateral 
symmetry and from which might be derived 
the divergent groups, viz., the coiled snail on 
the one hand and the naked slug on the other. 
One may readily observe a similarity in 
the structure of spawn as well as in larval 
peculiarity in species of the same genus and 
more so, perhaps, if the species are closely 
related. Such a condition may then parallel 
to a large extent the taxonomic position as- 
signed to the adult forms and, therefore, be 
of taxonomic value. 
REFERENCES 
Korschelt, E., and K. Heider. 1900. Text- 
book of the embryology of invertebrates. 
Vol. IV. 594 pp. Swann Sonnenschein and 
Co., Ltd., London. 
Lebour, Marie V. 1932. Cowries. Nat. 
Hist. { New York} 32(2): 188-194. 
1934. The eggs and larvae of some 
British Turridae. Mar. Biol. Assoc. United 
Kingdom, Jour. 19(2): 541-554. 
1935. The breeding of Littorina neri- 
toides. Mar. Biol. Assoc. United Kingdom, 
Jour. 20(2): 373-378. 
