FREE INSTITUTE OF SCIENCE 
ON THE LIFE HISTORY OF AN ECONOMIC CUTTLEFISH OF JAPAN 
facts doubtless show that in these regions the spawning of the cuttlefish con- 
tinues throughout nearly the whole year. 
It is interesting that very young individuals with mantle length measuring 
only 60 mm. are in many places caught in plenty with fishing nets in March 
or April—a month in which, as seen from the tables above given, there is very 
little or no catch at all, for instance, in Hokkaid6é, Sado, Tsushima, etc. It 
follows, therefore, that these individuals may be derived from spawning of the 
previous autumn or winter, and grow at the rate as above mentioned during the 
succeeding summer and autumn. It is further true that they may become 
mature in a year. 
DEVELOPMENT OF MALE GENITAL ORGANS AND PAIRING 
SEASON 
The hectocotylus is the left ventral arm, of which the full-formed structure 
has already been described by Dr. Ishikawa (1913). 
The rate of its development varies to some extent in different localities. 
In Hokkaidé, as far as I have been able to ascertain, its transformation be- 
comes discernible for the first time in the male of about 190 mm. mantle length, 
while Oki males of 176 mm. mantle length show fairly distinct hectocotyliza- 
tion, so that compared at about the same stage, the transformation of the arm 
is generally further advanced in the specimens from Oki than in those from 
Hokkaidé. Moreover, in Hokkaidé occurrence of full-formed hectocotylus 
is confined to December, which represents, in this locality, the final part of the 
fishing season, whereas in Oki, so far, hectocotylized males may be caught 
nearly all the year round. These facts as to the hectocotylization are parallel 
with the development of the internal genital organs, as given in the following 
tables: 
Microscopic examinations show that the testis becomes mature when it 
attains a length of about 80 mm. As shown in the above tables, the testes 
of all the males from Oki are longer than this measurement and mature, and 
numerous spermatophores are found at any time of the year, while in Hokkaidé 
males provided with a testis so much developed are confined to December. 
It is thus evident that the maturation of the testis goes hand in hand with the 
hectocotylization so as to be ready for pairing. Such a seasonal contrast as 
between Oki and Hokkaidé, in respect to the maturity of the male genital 
