CRANIAL GANGLIA OF AMBLYSTOMA 495 



later become arranged on the median surfaces of the arches where 

 they form cartilaginous tissue. 



12. The wandering mass of 'mesectoderm' is of neural-crest 

 origin and in no region is it augmented by a contribution from 

 cells of the lateral ectoderm. 



13. The removal of neural crest in the branchial and hyoid 

 regions is accompanied by smaller external gills and marked 

 deficiencies in the branchial and hyoid cartilages. The hyohyals, 

 ceratohyals, ceratobranchials, epibranchials, and first basibranchial 

 are formed from the wandering neural crest, while the second 

 basibranchial is formed from mesoderm near the anterior wall of 

 the pericardial chamber. In the ganglionic regions the neural 

 crest appears to form only the general visceral components. 



14. The removal of neural crest in the trigeminal region shows 

 no complete absence, but deficiencies in the size of the quadrate 

 and mandibular cartilages. However, there is no doubt that 

 these cartilages are formed from crest cells. The regeneration of 

 the crest cells always occurred in the operation of these specimens 

 because they were necessarily confined to very early stages. 



15. The neural crest in the trigeminal region which migrates 

 over the anterior border of the optic vesicles apparently gives 

 rise to the anterior portion of the trabeculae. 



LITERATURE CITED 



Beard, J. 1885 The system of branchial sense organs and their associated 

 ganglia in Ichthyopsida. A contribution to the ancestral history of 

 the vertebrates. Quart. Jour. Micr. Sci., vol. 26, New Series. 



Brauer, A. 1904 Beitrage zur Kenntnis der Entwicklung und Anatomie der 

 Gymnophionen. IV. Die Entwicklung der beiden Trigeminusgang- 

 lien. Zoolog. Jahr., Suppl. Bd. 7. 



CoGHiLL, G. E. 1916 Correlated anatomical and physiological studies of the 

 growth of the nervous system of Amphibia. II. The afferent system of 

 the head of Amblystoma. Jour. Comp. Neur., vol. 25. 



Detwiler, S. R. 1917 On the use of Nile blue sulphate in embryonic tissue 

 transplantation. Anat. Rec, vol. 13. 



DoHRN, A. 1902 Studien zur Urgeschichte des Wirbeltierkorpers. XXII. 

 Weitere Beitrage zur Beurteilung der Occipitalregion und der Gang- 

 lienleiste der Selachier. Mitteil. aus der Zoolog. Station zu Neapel, 

 Bd. 15. 



THE JOURNAL OF EXPERI.\IENT.\L ZOOLOGY, VOL. 35, NO, 4 



