THE CRANIAL GANGLIA IN AMEIURUS 369 



are in such close proximity to the large lateral mass ganglion 

 of the Xth that general visceral fibres might easily grow into the 

 nerves, so that we cannot infer the presence of lateral mass cells 

 simply because general visceral fibres may be in the peripheral 

 nerves of these ganglia. The IXth is unique in that neither 

 general visceral fibres nor lateral mass cells have been found in its 

 composition. 



Aside from the explanation given above, there seems to be no 

 reason for the presence of the epibranchial placodes in the head, 

 and for the part they play in contributing cells to those ganglia only 

 which supply fibres to gustatory organs. The gustatory organs 

 are all innervated from the cerebral ganglia, and only those cere- 

 bral ganglia give rise to gustatory fibres which contain cells derived 

 from the epibranchiaJ placodes, and the ganglion which seems to 

 give raise to gustatory fibres only seems also to come only from the 

 epibranchial placode. 



My series at this stage are taken four hours apart, and the epi- 

 branchial ganglion acquires a connection with the proximal por- 

 tion of the lateralis IXth (figs. 58 and 59) before losing its connec- 

 tion with the epidermis. However, the growing point of the 

 epibranchial root is extremely thin. It passes up internal to the 

 cardinal vein, which is in striking contrast with the growing parts 

 of the epibranchial ganglia of the second and third true gills which 

 pass up toward the brain external to the same vein (figs. 65, 66. 

 67, 68, and 69) . The growing point of the IXth between the thicker 

 portion derived from the epibranchial placode and the lateralis 

 IXth, is shown in fig. 58. In the preceding series (75 hours) this 

 connection is only one cell thick and in an embryo of 69 hours it is 

 entirely absent. 



THE ORIGIN OF THE LATERALIS IXth GANGLION 



After reaching the level of the auditory vesicle in its dorsal 

 extension, the growing point of the root of this epibranchial gan- 

 glion comes into contact with a mass of cells derived from the pos- 

 terior and ventral portion of the auditory vesicle, which later 

 forms the lateralis ganglion of the IXth. It is not derived from 



