1866.] 



of the Optic Lohes of the Cuttle-Fish, 



261 



nucleated cells, with "which filaments of the optic nerves are connected. 

 The second or middle layer is composed entirely of fine nerve-fibres which 

 form two sets — one vertical, and the other horizontal. The vertical fibres 

 issue at the under surface of the first layer from the network which its 

 nuclei form with the fibres of the optic nerves. Some are continuous with 

 the horizontal fibres, but the majority continue downward across them to 

 the third or inner layer. At the junction of these two layers is a row of 

 nucleated cells which send thin processes in different directions, and with 

 which some of the nerve-fibres are connected. The third or inner layer is 

 composed entirely of closely- aggregated nuclei, which are joined together 

 in a network by the fibres which issue from the under surface of the middle 

 layer. 



The cortical substance, consisting of these three layers, forms only a very 

 small portion of the optic lobe. Out of the nuclear network of the inner 

 layer fine nerve-fibres descend into the body of the lobe which it encloses. 

 At first these fibres are vertical, parallel, and arranged in uniform series, 

 with scattered nuclei between them ; but as they descend to the centre of 

 the lobe, they diverge more and more, and cross each other to form a 

 plexus, first with oval and then with broader m^eshes, in which the nuclei 

 and nucleated cells are collected into groups of corresponding shape and 

 size. 



From the plexus at the inner side of the lobe bundles converge from all 

 parts to form the lower half of the peduncle, the upper part of which 

 consists of masses of small nuclei, and gives attachment, by a short pedicle, 

 to a small tubercle. This tubercle consists of closely-aggregated nuclei 

 connected by fibres which converge to its neck and escape into the peduncle 

 of the optic lobe. 



x\fter concluding his description of the optic lobes, the author gives a 

 short account of the structure and connexions of the remaining cerebral 

 ganglia of the Cuttle-fish, with the view of determining their homologies. 



From the nature of the parts which it supplies, the foremost or pharyn- 

 geal ganglion would seem to combine the function of the centres which give 

 origin to the trigeminal, the olfactory, and the gustatory nerves in the 

 vertebrata. The second bilobed ganglion appears to correspond partly to 

 the cerebral lobes and partly to the cerebellum of fishes. The posterior 

 portion of the suboesophageal mass is the analogue of the medulla oblongata ; 

 while the anterior portion may be regarded as the spinal cord concentrated 

 below the oesophagus and in the neighbourhood of the feet, which derive 

 all their nerves from that source. 



