512 p. E. SMITH 



ters (Wilder '99, '04, and Hilton '04, '09) have been noted. This 

 species also develops under conditions which are rather unusual 

 for the tailed amphibia, namely, the space in which each larva 

 develops is very limited; this, together with an unusually large and 

 dense yolk mass, causes a twisting of the embryo and a marked 

 reduction in the size of the cavities. These latter conditions are 

 evidently largely contributory to the various modifications which 

 will be noted. 



MATERIAL AND METHODS 



Various features in the development of the nervous system have 

 been traced from the first appearance of the medullary plate 

 (about 00 hours) to the adult. For convenience the developing 

 eggs and larvae up to the time of hatching have been divided into 

 twelve stages. As a large number of eggs in each stage have been 

 secured and as it was impossible for the specimens placed in any 

 stage to be at exactly the same degree of development, a practi- 

 cally continuous series from the first appearance of the medullary 

 plate up to the time of hatching has been secured. This is especi- 

 ally true of Stages VI to XL 



Several fixers have been used, namely: Gilson's, Zenker's, 

 Flemming's (stronger sol.), Hermann's, Perenyi's, HgCL plus 

 glacial acetic acid, platinic chloride (0.25 per cent), and form- 

 alin f 10 per cent). Formalin was found to be the most satisfac- 

 tory fixer for both section and surface study. It differed from the 

 other fluids used in that good fixation could be secured although 

 the egg membranes were present. 



Celloidin imbedding was used throughout for the stages up to 

 hatching. Due to the density of the yolk satisfactory results with 

 paraffin could not be secured and double imbedding with paraffin 

 and celloidin was not as successful as the celloidin alone. 



Most of the series were stained with hematoxylin (chloral and 

 Delafield's) and eosin. As the work was largely morphological, 

 a series of models have been made and from these the relations of 

 the various sections can be secured. 



