382 F. L. LANDACRE 



The spinal ganglia derived from the neural crest furnish both 

 general visceral and general cutaneous fibres, but these two com- 

 ponents are combined in the same ganglion, although probably 

 having separate terminations in the cord. In the head, however, 

 we have the lateral mass ganglion of the Xth, which probably cor- 

 responds to the neural crest ganglion of other types, differentiated 

 into two ganglia, a general cutaneous, the jugular, situated intra- 

 cranially, and an extra-cranial portion that is in all probability 

 the general vesceral ganglion. 



From the preceding description it will be seen that there are 

 two quite distinct sources of origin for the cerebral ganglia in 

 Ameiurus, the lateral mass and the epibranchial placodes. Un- 

 like most types, there is no well defined neural crest. The lateral 

 mass early gives rise to the dorso-lateral placodes represented by 

 the auditory vesicle and the pre- and postauditory placodes, while 

 the remainder of the lateral mass gives rise to the primordia of 

 ganglia and to mesectoderm. The lateral mass doubtless con- 

 tains beside the dorso-lateral placodes the homologue of the neural 

 crest of other types, but the greater portion goes to form mesecto- 

 derm. 



Of the components found in the adult ganglia, the special vis- 

 ceral or gustatory come from the epibranchial placodes, while 

 the general visceral come from the ventral portion of the lateral 

 mass. The general cutaneous component comes from the lateral 

 mass also, but typically from the dorsal portion, as in the case of 

 the jugular ganglion. The acustico-lateralis component shows its 

 kinship to the general cutaneous component in that the lateralis 

 ganglia of the Vllth come from the lateral mass. The auditory 

 and lateralis IXth come chiefly from the auditory vesicle but may 

 have lateral mass cells in their composition. They show a some- 

 what more specialized mode of origin, while the lateralis Xth 

 comes entirely from the postauditory placode and is the most 

 highly specialized in mode of origin of the acustico-lateralis gan- 

 glia. The geniculate ganglion was seen to be composed of con- 

 stituents from both the ventral portion of the lateral mass and 

 from the epibranchial placodes. 



