57 

 on th5 crani^il r^presantati.v's of the dorsal oornu, the ggnernl 

 cutansoiis aucleus. This fact caa only be taken to mean that 

 the tuberculum aoustioim is phylogeneticalLy the younger of 

 the two straotares in question. In Subsection ^ it was shown 

 that the general cutaneous nucleus has the archaic structural 

 features of the dorsal cornu cappei with a molecular layer 

 continuous /?ith the cerebellar crest of the acusticum; and that 

 there are present here both the molecular cells and the neu- 

 rones of Purkinje. ^!oa' this structural continiiity iiay signi- 

 fy that the acusticun has been derived fron the general cuta- 

 neous nucleus in the phylogeny of the vertebrate nervous sys- 

 tem. Of course it flill be necessary to have a thorough study 

 of the embryology of this region in the lower vertebrates before 

 such a conclusion can receive unqualified support. Then, too, 

 the rise of the tuberculum acusticum has been but one feature 

 in the evolution of the lateral line system as a whole, and 

 so tie may confidently expect some assistance from the further 

 study of the affinities of its sense-organs. 



There is somewhat more solid ground for the belief that 

 the tuberculum acusticum has itself given origin to a very 

 important region of the brain, the cerebellum. The full ev- 

 idence on this point ^vill be presented in Section \', Subsec- 

 tion *5. 



