486 L. S. STONE 



placode is a mass of crest cells near the ectoderm and epibran- 

 chial placode of X. These are crest cells which possibly give 

 rise to a portion of the visceral ganglion, for when followed ven- 

 trally they lie close to the epibranchial placode of X. 



A specimen killed five days after operation shows on the 

 operated side a large normal lateral-line ganglion. The placode 

 of the lateral-line ganglion of IX seems to be a little less advanced 

 in development than on the normal side. Farther ventrally 

 (fig. 88) loose masses of cells are being given off from the epi- 

 branchial placodes of IX and X and are not of crest-cell origin, 

 for there are no crest cells in the branchial region of the operated 

 side. 



A specimen killed eight days after operation shows a large 

 vagus lateral-line ganglion, in front of which is a portion of a 

 small visceral ganglion. The ganglia are still made up of loose cells 

 and nerve fibers from the visceral ganglia cannot be determined. 

 Posterior to the auditory vesicle on the operated side is a small 

 lateral-line ganglion which lies above the small visceral ganglion 

 of IX which is connected with the epibranchial placode. Only 

 a very few scattered crest cells appear on the median surface of 

 the mesoderm of the branchial arches. A number of other 

 specimens killed between eight and ten days after operation 

 show small visceral ganglia, which are derived from the epibran- 

 chial placodes, and perfectly normal IX and X lateral-line ganglia. 

 In these cases also there are only a few loose crest cells in the 

 branchial region on the operated side. 



A typical specimen killed eleven days after operation shows a 

 large vagus lateral-line ganglion with the ramus lateralis superior 

 vagi nerve extending posteriorly to innervate the body line of 

 sense organs (fig. 89). The anterior portion of this ganglion is 

 part of the visceral ganglion of X. From it pass slender fibers to 

 the epithelium of the second external gill and also a number of 

 motor fibers to the branchial trunk of the vagus can be seen in 

 the second branchial arch. It gives off motor fibers to the bran- 

 chial muscles, and when followed ventrally into the branchial 

 arch it is lost near the epithelium on the pharyngeal side. There 

 is no definite second branchial trunk. As the superior lateralis 



