234. PROFESSOR F. M. BALFOUR. 



cords, so that a section through the supra-oesophageal ganglia 

 has an obvious resemblance to what would be the appearance 

 of a section through the united ventral cords. On the outer 

 borders of the ganglia the cells extend upwards, but they end 

 on about the level of the optic nerve (fig. 19 d). Immediately- 

 dorsal to this point the fibrous matter of the brain is exposed 

 freely on the surface (fig. 19 a, b, 8cc., a). I shall call the region 

 of fibrous matter so exposed the dorso-lateral horn of white 

 matter. 



Where the two ganglia separate in front the ganglion cells 

 spread up the inner side, and arch over so as to cover part 

 of the dorsal side. Thus, in the anterior part, where the two 

 ganglia are separate, there is a complete covering of ganglionic 

 substance, except for a narrow strip, where the dorso-lateral 

 lobe of white matter is exposed on the surface (fig. 19 a). From 

 the point where the two ganglia meet in front the nerve-cells 

 extend backwards as a median strip on the dorsal surface (fig. 

 19 D and e). This strip, becoming gradually smaller behind, 

 reaches nearly, though not quite, the posterior limit of the 

 junction of the ganglia. Behind it there is, however, a region 

 where the whole dorsal surface of the ganglia is without any 

 covering of nerve-cells. 



This tongue of ganglion cells sends in, slightly behind the 

 level of the eyes, a transverse vertical prolongation inwards 

 into the white matter of the brain, which is shown in the series 

 of transverse sections in fig. 19 e, and also in the vertical longi- 

 tudinal section (PI. XVIII, fig. 21), and in horizontal section 

 in PI. XVIII, fig. 22. 



On the ventral aspect of each lobe of the brain there is pre- 

 sent a very peculiar, bluntly conical protuberance of ganglion 

 cells (PI. XVIII, fig. 22), which was first detected by Grube 

 (No. 10), and described by him as ''a white thick body of a 

 regular tetrahedral form, and exhibiting an oval dark spot in 

 the middle of two of the faces." He further states that it is 

 united by a delicate nerve to the supra-oesophageal ganglion, 

 and regards it as an organ of hearing. 



In Peripatus cape n sis the organ in question can hardly 



