1. Gonad and body weight records have been collected for 487 individual octopuses over a period of 3 years.
2. In the size range used for experiments (200-1000 g.), the ovary is always immature in control animals, and constitutes only about 1/500th of the total body weight. The testis is rather larger, generally ripe, and forms about 1/100th of the body weight, increasing somewhat relative to the size of the body over the range considered.
3. Following optic nerve section, or removal of certain parts of the supraoesophageal lobes, the gonads enlarge. In females the ovary enlarges from 1/500th to as much as 1/5th of the total body weight within 5 weeks of operation and this may be followed by laying of fertile eggs that are brooded in a normal manner. In males where the testis is generally mature before operation the enlargement produced is only of the order of 50%.
4. Enlargement of testis or ovary is always accompanied by enlargement of one or both of the optic glands, and operational treatments that normally cause enlargement of the gonad are ineffective if the optic glands are first removed.
5. The optic glands are innervated from the subpedunculate/dorsal basal area in the hind part of the supraoesophageal brain mass. Lesions in this area, or severance of the nerve tracts running along the sides of the brain from it to the optic glands, cause these and the gonads to enlarge.
6. Unilateral central lesions or optic nerve section cause optic gland enlargement on the operated side only, but appear to be as effective in determining gonad enlargement as bilateral treatments.
7. It is concluded that maturation of the gonad is determined by secretion from the optic glands which is normally held in check by an inhibitory nerve supply from the subpedunculate/dorsal basal lobe area. The action of this region is in turn dependent upon the integrity of the optic nerves and thus, presumably, upon light.
8. This system in cephalopods is compared with analogous systems regulating sexual maturity in arthropods and vertebrates.