228 



C. JUDSON HERRICK 



All of these measurements were made on the gross specimens 

 except that of series CIII, made from microscopic preparations. 



Measurements in millimeters of seven Necturus brains 



The variations in these measurements are naturally large, 

 but it is evident that the proportions of the reconstruction here 

 shown in figure 63 fall within the limits of variation shown by 

 the gross specimens. In this figure the distance (a) is below 

 the average and in McKibben's figure 5 ('11) this distance is 

 above the average. These variations are doubtless in part 

 due to distortion in preparation, but probably in life the varia- 

 tions are very large. 



The ventricular surfaces of specimens 1, 2, and 3 of McKib- 

 ben's series of 1917 were carefully studied under the stereo- 

 binocular microscope and the drawing, figure 63, was controlled 

 in all details from these specimens. This figure, therefore, 

 represents a composite of the data derived from sagittal micro- 

 scopic sections and the gross appearance of six half brains, the 

 outline being based in the first instance on the microscopic 

 sections. 



In this pattern we recognize a number of massive thickenings 

 of the lateral wall of the brain tube separated by sharp ventric- 

 ular sulci which mark lines where the wall is thinner. The 

 thickenings in general represent centers of greater proliferation 

 of nervous elements in the embryo and regions of greater func- 

 tional activity in the adult. Their pattern is in large measure 



