1. In Decapod Cephalopods there is a system of giant fibres probably serving to produce the rapid contractions of the mantle muscles and ink-sac by means of which the animal shoots backwards behind a cloud of ink.

2. The giant fibres in the stellar nerves arise in the stellate ganglion, not from single giant cells, but as syncytia, by the fusion of the processes of a large number of cells. In Loligo forbesi all the cells giving rise to the giant fibres of the stellate ganglion are connected together into a giant fibre lobe.

3. In Octopods there are no giant fibres, but in the position of the giant fibre lobe there is a small closed vesicle, pigmented yellow in some species, and named the epistellar body.

4. In the walls of this body there are curious cells, the neurosecretory cells, whose general structure resembles that of neurons, but whose inner processes (axons) end blindly, embedded in a homogeneous substance which fills the cavity.

5. The neurosecretory cells are innervated by a small nerve which reaches them from the mantle connective.

6. After removal of both epistellar bodies from Eledone moschata the animal shows general muscular weakness for some days.

7. It is suggested that the epistellar body has arisen from the giant fibre lobe, and that the neurosecretory cells produce at their inner ends a secretion which is poured into the bloodstream.

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