384 F. L. LANDACRE 



and nerves, with the single exception that we have portions of 

 the acustico-lateralis ganglia, as shown in other types, arising 

 from the same source as the general cutaneous. This is to be 

 explained on the basis of the relationship of the two components. 

 In sharp contrast with this, however, we have distinct sources of 

 origin for the special and the general visceral ganglia which are 

 combined in the preceding table (II) and which in the adult are 

 closely fused, particularly in the geniculate and in the posterior 

 portion of the tenth. 



The differences between the two tables may be summarized 

 briefly as follows: The visceral ganglia of the adult in table II 

 (p. 321) are broken down in the table V into those portions 

 derived from the epibranchial placodes, i.e., the special visceral 

 or gustatory ganglia, and the portions derived from the lateral 

 mass, i.e., the general visceral. 



The acoustico-lateralis ganglia of the adult in table II are 

 broken down in table V into those portions derived from the 

 lateral mass, i.e., the lateralis Vllth and possibly portions of 

 the vTIIth ganglion and of the lateralis IXth, and those portions 

 derived secondarily from the auditory vesicle and placodes, i.e., 

 all of the lateralis Xth and most if not all of the auditory and later- 

 alis IXth ganglia. 



GENERAL SUMMARY 



1 . The neural plate in Ameiurus differentiates longitudinally 

 into three regions: a median region, the neural keel, which later 

 becomes the neural tube, and two lateral regions, the lateral masses, 

 separated from the neural keel by constricted areas. 



2. After the body has assumed a rounded form, the lateral 

 masses come to lie on the sides of the body still retaining their 

 connection with the neural cord by constricted areas. Part of the 

 lateral mass on either side differentiates into the auditory vesicle 

 and the pre- and postauditory placodes, which are extensions of 

 the vesicle and resemble it in structure. These represent the dor- 

 so-lateral placodes of other authors. The remainder of the lateral 

 mass breaks down more or less completely into loose tissue in 



