Johnston, Morphology of the Head. 247 



clined to think that the olfactory organ and nerve are peculiar 

 in the vertebrate organization. In the figures, however, these 

 structures have been indicated by the same symbols as the vis- 

 ceral sensory system, on the basis of the visceral function of the 

 olfactory apparatus. 



On the basis of their function the writer has for several 

 years felt impelled to seek some morphological connection or 

 relation between the olfactory apparatus and the visceral sen- 

 sory, especially the gustatory. After what has just been said 

 this search would seem contradictory, if not fruitless. However, 

 we have not yet sufficient knowledge of these systems to war- 

 rant our jumping to any final conclusion. Even if the first seg- 

 ment of the vertebrate body is a prostomium, its general cu- 

 taneous innervation is homologous with that of tiie rest of the 

 body. May not its visceral sense be related to that of the typ- 

 ical segments also? The writer has in his notes detailed state- 

 ments of several hypothesis, but it will be more profitable in the 

 present state of our knowledge to indicate briefly one or two 

 lines along which facts may be sought, than to spend time in 

 speculations. 



(i). When the gustatory paths and centers within the 

 brain are known at least as well as we know the olfactory we 

 may find some indications of their relationship. 



(2). If we were to apply to the epibranchial placodes the 

 theory of Kupffer which the writer has declined to accept for 

 the dorso-lateral placodes, some such line of reasoning as this 

 might be developed. The cells of the chemical sense which are 

 scattered over the body in annelids may have collected over the 

 gill slits in primitive vertebrates. These collections would form 

 the primary sense organs of Kupffer. These sense cells sink 

 below the surface as ganglion cells. Secondary sense organs 

 develop in the placodes and these become the taste buds. If 

 we suppose that the primarj^ sense cells sent their fibers to the- 

 brain along with the general visceral rami which pass adjacent 

 to the gill slits, we have a close relation shown between the 

 gustatory and olfactory systems. It should be noticed, however, 

 that in this statement as it stands no homology is shown be- 



