494 L. S. STONE 



before the appearance of the placode, the supra-orbital line of 

 sense organs is absent as well as a large part of the VII lateral- 

 line ganglion. The small remaining VII lateral-line ganglion in 

 such cases gives rise to lateralis fibers, which innervate the group 

 of sense organs on the lower jaw, and also slender fibers to the 

 infra-orbital group. 



4. The supra-orbital primordium of lateral-line sense organs 

 arises from the anterior extremity of the VII lateral-line ganglion 

 placode. 



5. The supra- and infra-orbital and hyomandibular primordia 

 of lateral-line sense organs have separate seats of origin. 



6. The ventral hyomandibular and mandibular groups of 

 lateral-line sense organs also appear to have separate seats of 

 origin. 



7. The epibranchial placodes of VII, IX, and X give off cells 

 which become incorporated in the visceral ganglia, and when 

 these placodes are removed from the ectoderm in early stages 

 (23-26) no special visceral ganglia nor gustatory fibers can be 

 found. 



8. The complete removal of ectoderm in the region of IX and X 

 which includes all the primordia of the lateral-line system is 

 accompanied by a complete absence of lateral-line ganglia. 

 When only partially removed, small lateral-hne ganglia are 

 produced. 



9. Large areas of ectoderm removed from the region of IX and 

 X also show an absence of cutaneous fibers as well as visceral 

 sensory fibers. 



10. The lateralis and special visceral ganglia are derived en- 

 tirely from placodes, and the general cutaneous, for the most 

 part if not entirely, is also derived from placodes. 



11. The neural crest cells arise from the dorsal portion of the 

 neural tube at the points of the fusion of the neural folds. They 

 can be distinguished as early as the closure of the folds, and from 

 this region they can be followed by their difference in pigmentation 

 from the surrounding tissue and by the presence of small yolk 

 granules in their cytoplasm as they descend upon the mesoderm 

 of the visceral arches around which they wrap themselves and 



