PREES INST EROUDE*OR SCIENCE 
ON THE LIFE HISTORY OF AN ECONOMIC CUTTLEFISH OF JAPAN 
19 
shows the results of the observations carried out, just at the beginning of the 
catch, by an official experimental boat along a line extending 100 miles off the 
coast. A warmer water of the Tsushima Current, the lowermost stratum of 
which is nearly of the temperature best suited for the cuttlefish to live in, is 
found, as seen in the section, close to the coast, being very probably pressed 
from the oceanic side by a big body of colder bottom water of the Japan Sea. 
As mentioned before, the warmer water of the Tsushima Current comes 
out into the Pacific side of the northern part of Honshiu, passing through the 
Tsugaru Strait and bathes the coast of Iwaté-ken. In this place, when the 
current is strong as in summer, it extends over the Oya-shiwo of the offing, and 
when the latter is enlarged as in winter, the former is compressed into a narrow 
zone towards the shore. The seasonal population of the cuttlefish in this 
prefecture is much connected with this relative strength of these two currents. 
Fic. 7. 
Hydrographic section off Shimané-ken, showing vertical distribution of temperature on July 14-15, 
1919 (from a hydrographic observation made by the Fishing Experimental Station of Shimané-ken). 
This is shown by an unusually good catch taking place 5-10 miles off the coast 
in the latter part of October of last year, when an official boat of the local 
government was carrying out, along a line extending 80 miles off the coast, 
observations the results of which are represented in the section shown in fig. 8. 
There appears close to the shore in the section a zone of warmer water of 12° 
16° C. which represents nothing but the said branch of the Tsushima Current 
inhabited by the cuttlefish. In the offing there is a large water body illustrated 
by isothermal lines of 4°C.and 8° C.; this is probably the Oya-shiwo, which is of 
a temperature lower than that best for the creature under consideration. This 
current which was just enlarging at that time, as occurs usually in later autumn, 
seems to have strongly pressed the warmer current against the shore into a 
narrow, but deep vertical zone of roughly 10 to 20 miles in breadth, where the 
said good catch was made. Under such a hydrographic condition it is probable 
