OF PERIPATUS CAPENSIS. 891 



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 shewn in the series of 

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

 tudinal section (PL 51, fig. 21), and in horizontal section in 

 PL 51, 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 (PL 51, 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-cesophageal ganglion, and regards it 

 as an organ of hearing. 



In Peripatus capensis the organ in question can hardly be 

 described as tetrahedral. It is rather, of a flattened oval form, 

 and consists, as shewn in sections (PL 50, fig. 19 C and D, d\ 

 mainly of ganglion cells. In its interior is a cavity with a distinct 

 bounding membrane : the cells of which it is composed vary 

 somewhat in size, being smallest near the point of attachment. 

 At its free end is placed a highly refractive, somewhat oval 

 body, probably forming what Grube describes as a dark spot, 

 half embedded in its substance, and kept in place by the sheath 

 of nervous matter surrounding it. This body appears to have 

 fallen out in my sections. The whole structure is attached to 

 the under surface of the brain by a very short stalk formed of a 

 bundle of cells and nervous fibres. 



It is difficult to offer any interpretation of the nature of this 

 body. It is removed considerably from the surface of the 

 animal, and is not, therefore, so far as I can see, adapted to serve 

 as an organ of hearing. 



The distribution of the white or fibrous matter of the ganglia 

 is not very easy to describe. 



There is a central lobe of white matter (fig. 19 E), which 

 is continuous from ganglion to ganglion, where the two are 

 united. It is smaller behind than in front. On its ventral side 

 it exhibits fairly well-marked transverse commissural fibres, con- 



572 



