CRANIAL GANGLIA OF AMBLYSTOMA 425 



final system. However, when one compares this description with 

 skin amounts of early stages of Amblystoma, another interpreta- 

 tion seems to be more plausible. No such pattern can be found 

 in Amblj^stoma embryos, but whenever the contour of underlying 

 structures makes its appearance on the surface certain transitory 

 thickenings appear due to mechanical molding, as one finds be- 

 tween somites, gill swellings, around the early optic vesicles and 

 the early limb bud. It seems possible, therefore, that most of 

 the earh^ pattern described in Necturus has no significance in the 

 formation of the lateral-line system. 



Neural crest. It is generally accepted that portions of the 

 cranial ganglia are derived from the neural crest; in fact, early 

 investigators of cranial nerve problems made the crest cells their 

 sole source of origin. Landacre ('10) would derive all general 

 cutaneous ganglia and the general visceral system exclusively from 

 neural crest. 



In view of the fact that there have appeared descriptions of 

 extensive wanderings of neural crest, it seems strange that so 

 little emphasis has been put upon such an outstanding feature. 

 The literature contains comparatively few descriptions of any 

 complete investigations of the growth of the neural crest outside 

 of its supposed connection with the formation of cranial ganglia. 

 In most of the descriptions of the early stages of developing 

 cranial ganglia the assumption that the crest cells were concerned 

 only with the formation of ganglia and nerves has been so general 

 that many investigators have been led to overlook the fact that 

 any further wandering of these elements occurs. However, 

 various careers have been assigned to them by a few investigators. 



Marshall (78), working on the chick, and van Wijhe ('82), on 

 the selachians, were among the first to observe that the anterior 

 part of the neural crest, which could not be identified with the 

 formation of ganglia, gradually disappeared. They could not 

 determine its final fate. Kastschenko ('88) went a step farther 

 in suggesting that the cells which were lost from the neural crest 

 did not degenerate, but added themselves to mesenchyme. Addi- 

 tional descriptions of the neural crest then followed, by Gorono- 

 witsch ('93) in birds and Piatt ('96, '97) in Necturus. Both 



