The Giant Nerve Fibres and Epistellar Body of Cephalopods

AT the hind end of the stellate ganglion of E l e d o n e m o s c h a t a there is a small yellow spot, about the size of a pin's head, which can be seen on examination of serial sections to consist of a closed vesicle. On account of its position it has been named the epistellar body (Young, 1929). It has been found in all the Octopods examined, though it is not always coloured yellow. Search was made for a similar organ in the same position in Decapod Cephalopods but no trace of it could be found. However, during the search certain extremely large nerve fibres were noticed in the stellate ganglion of L o 1 i g o, and study of these showed them to originate not from giant nerve cells, but by the fusion of the axons of a very large number of small cells which are congregated together in a separate lobe situated at the hind end of the ganglion. This lobe lies in a position which corresponds exactly to that of the epistellar body present in Octopods, and these latter have no giant fibres. The conclusion which has been drawn as a result of study of the two systems is that the epistellar body of Octopods is derived from the cells of the giant fibres of Decapods; and, since the former is probably secretory, we have