THE NERVOUS SYSTEM OF AMPHIBIA 165 



one-half the number of the whole system in the spinal cord. By- 

 actual count there are on one side of the non-motile embryo 210 

 of these cells; in the embryo of the early-flexure stage, 222; in 

 the embryo of the coil stage, 197; in the embryo of the early- 

 swimming embryo, 253. 



Except for the lower number in the coil stage there would ap- 

 pear in this series a gradual and progressive increase in the number 

 of cells during the period under investigation. Indeed, such an 

 increase in clearly differentiated cells probably occurs, for it is 

 my judgment that the reduced number observed in the embryo 

 of the coiled-reaction stage is due to the fact that the staining 

 of this specimen is not well adapted to the differentiation of these 

 cells from others around them. This is a misfortune from the point 

 of view of this paper, and it should be mentioned that the four 

 typical embryos were not selected for the projection of this sys- 

 tem of neurones alone. They were selected upon more general 

 considerations and the projections were made for the general 

 purposes of the more comprehensive study that is in progress. 

 The giant ganglion cells have simply been sketched into the pro- 

 jected outlines of the nervous and muscular systems which are 

 being used for other phases of the work. 



In the distribution according to regions it is found that within 

 the range of the first eighteen post-auditory myotomes, which may 

 be regarded as constituting the trunk, there are 149 giant-gan- 

 glion cells in the non-motile embryo; 150, in the early-flexure 

 embryo; 128, in the coiled specimen; 176, in the embryo of the 

 swimming stage. Caudad of this there are 61 in the non-motile; 

 72, in the early-flexure; 69, in the coil stage; 77, in the early- 

 swimming stage. 



Too great meaning should not be attached to the numerical 

 details of these counts for, while the cells were counted with 

 great care, the specimens were not prepared with a view to equiv- 

 alent differential staining of these elements in all cases. It hap- 

 pens, however, that the youngest and oldest members of the 

 series received essentially the same fixation and staining, and may, 

 therefore, be regarded as of equal value for makmg satisfactory 

 counts. The numbers of cells found, in these two specimens may 



