610 L. H. GOUGH. 



lies "1 mm. from the surface; its inner surface abuts on tlie 

 commissures. On the side of the group which is turned to- 

 wards the abdomen^ the sheath covering the radial support- 

 ing-fibres and the germ-cells forming the group are as before, 

 but the cells forming the tube have multiplied rapidly, and 

 now reach as far as the cells forming the group. On the 

 anterior side all parts of the group have multiplied their cells 

 to such an extent that they build a solid mass of nuclei, 

 reaching from the surface to the commissure. In this mass 

 only the nuclei of the sheath can be distinguished from the 

 others. The interior of the epidermis-tube is now filled with 

 supporting fibres. 



From the interior surface of the nucleiferous mass are 

 seen in parts nuclei wandering through the commissural 

 part of the brain, the "Punktsubstanz ; " these afterwards 

 form a cellular layer on the dorsal side of the commissures, 

 which had been hitherto only covered by the mesodermatic 

 inner skin mentioned at the beginning of this description. 

 That the whole of the post-oral ventral ganglion-cord is 

 formed in the manner just described is proved by the 

 presence of numerous remains of tubes, filled with tangled 

 masses of supporting fibre, in the brain-mass. Each such 

 tube denotes the place where there was such a group of cells 

 during the earlier development of ihe cord. Later on the 

 tubes become entirely obliterated. These groups of cells, 

 with their radial supporting fibres, their sheaths and 

 tubes, possibly represent what Patten (34) compares to 

 omniatidia in his description of the development of the 

 brain of Arthropods. The comparison with sense-organs 

 is certainly very good. I find, however, more resem- 

 blance with the " Hiigelorgane der Seitenlinie," as 

 described by Leydig for fishes, and by the Sarasins (40) 

 for the l.arvEe of Amphibians. Judging by Patten's figures, 

 however, I must conclude that he saw a phenomenon in part 

 different to that which I have just described. In his 

 drawing one sees that each segment of the brain is composed 

 of several sense-organs, with larger ones in the middle line. 



