:310 The Ohio Journal of Science [Vol. XX, No. 8, 



tube and later erupted. Whichever of these three modes is 

 followed, the end result anatomically is the same. The excep- 

 tional behavior of the profundus ganglion must, of course, be 

 kept in mind. 



3. The acoustico-lateral system of ganglia and nerves arises 

 from the dorso-lateral placodes, which, however, are subject 

 to certain marked variations in time and in relation to other 

 placode like thickenings that make this generalization somewhat 

 less valuable than it seems. 



4. The gustatory ganglia arise from the third series of 

 placodes, the epibranchial. These are not to be considered as 

 ■old sense organs phylogenetically, but simply as ganglion 

 forming structures. 



5. The two special senses, the olfactory and the optic, are 

 such striking variations from the three ganglion forming series 

 mentioned that it does not seem best for the present to attempt 

 to incorporate these with the three series. They are best 

 treated separately, in which case we must establish five types 

 ■of behavior which the ectoderm undergoes in forming sensory 

 conductors between the periphery and the central nervous 

 system, (a) The neural crest ganglia furnishing general somatic 

 and general visceral nerves, (b) the dorso-lateral placodes 

 furnishing acustico-lateral fibers, (c) the epibranchial placodes 

 furnishing gustatory fibers, (d) the olfactory or permanent 

 skin placode furnishing olfactory fibers, (e) the optic or brain 

 placode furnishing optic fibers. 



Ohio State University, Columbus, Ohio. 



