Study on embryogenesis in the cephalopod.

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1. A normal table of embryonic stages for the pygmy cuttlefish, Idiosepius pygmaeus paradoxus, a suitable material for developmental study of the cephalopod,is presented. A female cuttlefish kept in still sea water in a small vessel repeatedly lays 30-80 fertilized eggs every 2 - 7 days for more than a month. Thirty stages are morphologically defined during the embryonic period from oviposition to hatching. Hatching occurs 16 - 18 days after oviposition at 20゜C. The external shape and some internal structures of the living embryo at each stage are illustrated, and the chronological ages and main developmental events are assembled in tabular form.2. The swelling process of the egg capsule in the cuttlefish, Sepiella japomica, was analysed during development. The weight of the whole egg decreased for 8 days after oviposition due to the loss of gelatinous coat in the capsule. After the appearance of perivitelline fluid in the egg, the weight of the whole eggagain increased linearly in parallel with the enlargement of perivitelline space, which was mainly caused by water intake. The difference of osmotic pressure between perivitelline fluid and sea water was about 135 mmol/kg at either the initial or later stages of development but it fell transiently less than 100 mmole/kg from stage 29 to 33. The protein content of the perivitelline fluid increased linearly during development, suggesting the production of osmoactive substance by the embryo.