378 F. L. LANDACRE 



The condition here seems to throw some light on the interpre- 

 tation given these placodes by former workers. They have so 

 often been described as arising at the time the neural crest gan- 

 glion fuses with the epidermis that I am unable to reconcile the 

 conditions existing, under which the placodal ganglia of the IXth 

 and first two divisions of the Xth arise in Ameiurus, with these 

 descriptions, unless there are neural crest cells in the IXth and 

 first two divisions of the Xth, which fuse with the epidermis in 

 an early stage in these types. Until the nerve components have 

 been thoroughly worked out in these types in which the neural 

 crest ganglia have been described as entering into the IXth and 

 first two anterior divisions of the Xth, so that we can be sure as 

 to whether there are general visceral fibres in these nerves, it is 

 useless to speculate as to either their mode of origin or composi- 

 tion. The presence of a neural crest in the region of the IXth 

 and Xth nerves, however, does not prove the presence of neural 

 crest cells in these ganglia, unless they can be definitely traced into 

 them. The absence of a lateralis ganglion and fibres in the IXth 

 nerve in Menidia (Herrick, '99) and apparently in Gadus (Her- 

 rick, '00, p. 296) and its presence in Ameiurus (Herrick, '01) 

 indicate how useless it is to speculate as to the composition of 

 these ganglia in one type because we know them in another which 

 is closely related. 



LATER HISTORY OF THE LATERAL MASS GANGLIA OF THE Xth 



There are two of these ganglia in Ameiurus: (1) the small 

 general cutaneous ganglion, the jugular, situated intra-cranially 

 (Herrick, '01, p. 210) . This ganglion is present in Gadus (Herrick, 

 '00, p. 297), where it is also intra-cranial. In Menidia, however, 

 the ganglion is small and wedged in between the visceral ganglia 

 and is extra-cranial. 



(2) Beside the j ugular ganglion there is the large visceral ganglion 

 situated extra-cranially over the fourth and fifth gill slits, the 

 earlier history of which was taken up with the postauditory lateral 

 mass. Some idea of its size at the time it comes into contact with 

 the placodes of the fourth and fifth gill arches can beobtained from 



