74 



capsule of the eye and below the optic ganglion. They supply the muscles 

 and capsule of the eye. 

 10. A pair of nerves arises from the front end of the ganglion and passes 

 forward with and under the pedo-propedal connectives. At the dorsal end 

 of the propedal ganglion each nerve turns sharpely downward over the 

 point of the pedal process and between the bases of the preorbital car- 

 tilages. It supplies the muscles at the base of the arms. 

 A pair of cells, (Text Fig. 16) the two largest and most remarkable cells 

 of the body are situated in the pedal ganglion. They lie near the median 

 hne a short distance in front of the statocyst. Each cell is fusiform and is 

 vertically placed. The nucleus is large , round , and central. The cytoplasm is 

 granular and , like the very large nerve process arising from it , stains diffe- 

 rentially with haemalum , taking a very distinct blue gray color , which is 

 in marked contrast to the other unstained fibres and cell bodies. The nerve 

 fibre arises from the backwardly curved upper end of the cell and passes 

 backward , upward and inward to the center of the visceral ganglion , where it 

 crosses the median line, forming a chiasma with the process of the other cell. 

 Beyond the chiasma the fibre passes into the viscero-stellate connective of the 

 side opposite its origin and , entering the steUate ganglion , divides into at least 

 four and probably five or even more branches , one of which enters each of the 

 larger nerves which arise from that ganglion , and thus the fibre branches pass 

 to various parts of the mantle. 



I have been unable to discover the ultimate distribution of the fibres or to 

 make out the central connections of the cell. These fibres, not previously 

 described in any mollusc, resemble closely the fibres of Mauthner in vertebrates 

 which are also unique in the nervous system of the animal, there being but 

 one pair of cells which are marked off both by the size of the cells and of their 

 fibres and by some chemical constituent which makes them stain differentially 

 from nearly ah other fibres. These cells appear in the embryo and persist 

 throughout life. The very size of the nerve processes has prevented their dis- 

 covery, since it is well-nigh impossible to believe that such a large structure 

 can be a nerve fibre. 



The propedal ganglion hes directly ventral to the pedal ganglion and between 

 the oesophageal canal and the muscles that are attached to the pedal process. 

 The connective which it receives from the pedal ganglion, is incompletely divided 

 into a central, and six pairs of lateral bundles. The ganglion is also connected 

 with the cerebral ganglion by the cerebro-propedal connective and with the 

 suprabuccal ganglion by the bucco-propedal connective. The former passes 



