426 L. S. STONE 



agreed that a greater part of the neural crest, augmented at the 

 margin of the gill clefts by a proliferation from the lateral ecto- 

 derm, becomes a wandering mass of ectodermal cells to which 

 Piatt gave the name 'mesectoderm' and that this wandering 

 mass of ectodermal cells is the origin of certain mesenchymal 

 tissue. It was Piatt, however, who suggested that the branchial 

 cartilages, surrounding connective tissue, and the anterior portions 

 of the trabeculae were derived from the 'mesectoderm.' In re- 

 spect to the branchial cartilages, this agrees with von Kuppfer 

 ('95) on Petromyzon, although he claims that the wandering ecto- 

 dermal cells are derived from deeper layers of ectoderm in situ. 

 Furthermore, Dohrn ('02), working on Torpedo, and Brauer 

 ('04), on the Gymnophiona, agree in the main with Piatt's 

 description of the mode of formation of branchial cartilages, but 

 they ascribe the sole origin of the cartilages to the neural crest. 



Recently Goette ('14) has discussed the formation and develop- 

 ment of the 'ectomesoderm,' as he calls it, in Siredon (Amblys- 

 toma tigrinum) which also illustrates what he finds in Petromy- 

 zon and Torpedo. He confines the anlagen of the ^ectomesoderm' 

 to the ectoderm in the regions of V, VII, IX, and X, which he 

 claims forms visceral skeleton, the outer gill muscles, and the 

 surrounding connective tissue. To the neural crest, epibranchial 

 placodes, and lateral-line placodes belongs the function of the 

 formation of the cranial ganglia and nerves. 



From this summary of the literature it is evident that there is 

 much disagreement concerning the formation of cranial ganglia 

 and the origin and further distribution of the wandering masses 

 of cells of ectodermal origin. 



In the light of these facts, an investigation of this problem was 

 suggested by Prof. R. G. Harrison on an animal, such as Amblys- 

 toma punctatum, which would lend itself to an experimental 

 analysis of all the factors involved. It gives me pleasure to 

 express here my appreciation to Doctor Harrison for his kind 

 criticisms and suggestions during its progress. 



Since the completion of the present investigation, there has 

 appeared a paper by Landacre ('21) on the fate of the neural crest 

 in Plethodon giutinosus, a urodele. In so far as the visceral 



