Johnston, Morphology of the Head. 197 



pression that Maurer is not primarily interested in the homol- 

 ogy of sense organs. He does not give much attention to end 

 buds and does not seem to realize the possibility that they may 

 not be homologous with lateral line organs. He overlooks end 

 buds in Petromyzon, but clearly distinguishes them from 

 lateral line organs in teleosts (p. 75-76). Only on p. 148, 

 in an unexpected connection, do I find an attempt to compare 

 the structure of end buds and lateral line organs with a view to 

 showing a genetic connection between them. After referring 

 to the distinction made by all authors between "birnformige 

 Sinnes- und fadenformige Stiitzzellen" he cites Leydig's belief 

 that both are sense cells. He then says: "Es ist also sehr 

 leicht moglich, dass lange Zeit diese beiden Zellformen spezi- 

 fische Sinnesfunktionen haben. Diese Auffassung wird durch 

 die Thatsache unterstiitzt, dass bei Knochenfischen in grosser 

 Verbreitung Hautsinnesorgane auftreten, welche nur aus einer 

 Zellform bestehen und diese Zellen gleichen vollkommen den 

 Stiitzzellen der hoher ausgebildeten Formen." Thus the gene- 

 tic relation of the two kinds of organs would rest upon the 

 homology of the sense cells of end buds with the supporting cells 

 of lateral line organs. If this is the only way to find a genetic 

 connection between the two kinds of organs, this fact itself 

 would seem to offer the strongest evidence against the proposed 

 homology. 



The discussion of the morphological and physiological re- 

 lationships of the visual and olfactory organs may best be re- 

 served to a later part of this paper (Sees. 13 and 15). 



6. The anterior e?id of the head. 



The importance of the question of the anterior end of the 

 head and brain can scarcely be exaggerated. It is evident that 

 whether we suppose the anterior end of the brain to be at the 

 so-called lobus olfactorius impar or in the region of the infun- 

 dibulum, the number of segments falling between that point 

 and, let us say, the III nerve would be greatly altered. Also, 

 a number of important structures which would be ventral in 

 position according to one view would be dorsal upon the other. 



