PLATES 1 AND 2 



EXPLANATION OF FIGURES 



56, 57, 58, 59 are graphic projections, made by the usual microscopical methods, 

 at a magnification of 100 diameters (reduced in the figures to 40 diameters), from 

 the Specimens 467, 473, 449 and 444, respectively. The methods of preparation of 

 these specimens have been described in connection with the figures 28 to 54. 



These figures show the projection of the central nervous system, the giant 

 ganglion cells, the lateral line primordia and the ectodermal thickenings that are 

 associated with the visceral pouches, in the four type specimens, 467, the non- 

 motile stage, figure 56; 473, the early-flexure stage, figure 57; 449, the coil stage, 

 figure 58; 444, the early-swimming stage, figure 59. 



224 



