Hei^rick, Gustatory Paths in Fishes. 



453 



companying diagram (Fig. 40) of the morphological relations. 

 Remembering that the secondary gustatory connections 

 are differentiations from the substantia reticularis grisea (the 

 anomalous position of the superior secondary nucleus being eas- 

 ily explained on mechanical grounds), we find here a natural 

 explanation of the further (tertiary) path to the inferior lobe, 

 for this is also a derivative of the substantia reticularis, crowded 

 for mechanical reasons in the opposite direction from that tak- 

 en by the secondary gustatory nucleus (cf. Johnston '02 a, p. 

 100). Turning now to the secondary olfactory connections, 

 the resemblance to those of the sense of taste is striking in fun- 

 damentals, in spite of great difference in detail. 



Fig. 40. Diagram showing ihe lelalioiis of the gustatory and olfactory 

 centers in teleosts, as represented by the shaded areas. Tlie black spots repre- 

 sent the position of commissures of secondary or tertiary fibers. 2, 3 and 4 rep- 

 resent the olfactory conduction paths of the second, third and fourth orders re- 

 spectively. II, III, IV represent the gustatory conduction paths of the second, 

 third and fourth orders respectively. Compare Figs. 38 and 39. 



The olfactory bulb, like the vagal lobe, contains a margin- 

 al zone of large secondary cells, the mitral cells, with long neu- 

 ritesand with dendrites which receive the endings of the per- 

 ipheral neurones. The interior of the bulb is filled with minute 

 intrinsic neurones. The secondary center is the area olfactoria 

 of the fore-brain, whose commissure bears the same relation to 

 the secondary tracts as do those of the secondary gustatory nu- 

 clei. The main tertiary tract passes, as before, to the inferior 

 lobe, which is, in fishes, the central correlation station for all 

 sensory impressions. The return path from the inferior lobe to 



