18 TRANSACTIONS OF WAGNER 
ON THE LIFE HISTORY OF AN ECONOMIC CUTTLEFISH OF JAPAN 
is a mixed water from three different sources, of which the relative propor- 
tions, of course, vary greatly according to different seasons. 
The Tsushima Current flows northward as illustrated by Schrenck and 
Makaroff, bathing the northwestern coast of Honshiu. At the northeastern 
part of the Japan Sea it is divided into two courses, one of which passes through 
the Tsugaru Strait to come out into the Pacific Ocean, and the other goes on 
its way still northward to bathe the western coast of Hokkaidé. It is a neces- 
sary consequence that the Pacific branch strikes against the Oya-shiwo, and 
then turns itself to the right side as is the rule in the Northern Hemisphere, 
taking for some distance a southern course parallel with the Oya-shiwo. It 
is this southern course that has a great significance for our present problem, 
for along the coast of Iwaté-ken the currents of different temperatures are put 
in an interesting hydrographic arrangement: the warmer current, 7. e., the 
said branch of the Tsushima Current passes nearer to the coast, as if pressed 
against the shore by the Oya-shiwo, the colder current. The relative strength 
of the two has much to do with the crop of some fishes. 
The second portion of the Tsushima Current turned northwards gives off 
a branch passing through the Soya Strait into the Okhotsk Sea, while the main 
current extends to the west coast of South Sakhalin to turn round, as it is 
highly probable, to contribute to the formation of the said Liman Current. 
Having given a rough sketch of the oceanic currents around the Japanese 
group of islands, we turn to inspect how these affect the distribution of the 
cuttlefish. Fig. 1 is a map intended to show the density of population of the 
animal. As the representation is simply based upon the statistical annual 
amount of catch, it is clear that the density shown with dots on the map does 
not exactly express the actual occurrence of the animal, but is represented at a 
measure lower than actual in some localities, for instance, as in the coasts of 
Yamagata-ken and Akita-ken, owing to comparatively small crop brought 
about by reason of several circumstances, under which the cuttlefish-fishing 
can not profitably be carried out. Putting aside such an apparent rupture 
of the zone of population, the density describes, first of all, a zonal curve with 
the densest part in coincidence with the extent of the Tsushima Current which 
contains in a proper depth of water strata of 10~-17° C. (fig. 7) favorable 
to the life of cuttlefish, as seen along the northern coasts of Honshiu and also 
on the coast of Shimané-ken, where a great catch of the cuttlefish was made 
throughout August of last year. The accompanying hydrographic section 
