220 Egbert Thompson Young, 



main lateral longitudinal nerves ofCystcercus pisiformis (since 

 the nucleus represents approximately the cell body exclusive of its 

 processes, and since it presents fairly definite outlines, I have 

 selected it for purposes of measurement instead of the very indefinite 

 cell): 4,2X2,1; 5,8X2,1; 5,0X2,5; 5,0X3,3; 4,2X2,5; 4,2X3,3; 3,7X2,5; 

 5,0X3,3; 4,2X2,1; 5,0X2,5; 5,0X2,5; 3,3X3,3. In making the above 

 measurements, those cells have been selected whose long diameter 

 lay in the plane of section. The following are measurements of the 

 small diameter of developing neurons from the lateral cephalic 

 ganglia of Cysticercus pisiformis (the long diameter was not 

 taken because the cell body was in no way marked off from the 

 nerve processes to which it gave rise) : 6,6, 2,1, 4,2, 5,0, 5,0, 6,6, 5,8, 

 4,2, 5,8, 5,0. The following measurements are of the lateral cephalic 

 ganglion cells in Taenia serrata (they are only approximate, for the 

 cell outlines are not clearly defined; the cell body is, however, a 

 little better differentiated from its processes than in the same 

 ganglia in Cysticercus pisiformis): 10,4X5,0; 4,2X3,3; 6,6X5,0; 

 9,2X5,8; 7,5X5,0; 5,4X3,7; 8,3X4,2; 8,3X5,0; 5,0X3,3; 8,3X6,6. 



These measurements show that marked differences of size as 

 well as form exists in the ganglion cells of Cysticercus pisi- 

 formis and Taenia serrata. Whether this difference is entirely 

 attributable to shrinkage of the cells under the action of fixatives, 

 as CoHN (1898) believes, is at least questionable. 



These differences can scarcely be ascribed to the eccentricity 

 of the plane of section relative to the main axis of the cell, because 

 in many cases at least, the plane passed thru both the nucleus and 

 more than one of the main processes of the cell. 



Apart from the brief statement of Bartels (1902, p. 552) that 

 "sich die drei lateralen Nerven unabhängig von einander aus demParen- 

 chym differenzieren", and the wholly general statement of Moniez 

 (1881) that all the organs of the Cestodes are formed from the 

 connective tissue, I have found no references in the literature to 

 the origin of the central nervous system. 



Concerning the histology of the developed nervous system, the 

 views are as divergent as numerous. While many of the earlier 

 authors saw and described this system in various Cestodes, it was 

 not until the time of A. Schneider (1873) that its function was 

 recognized, and until the present time there has been much dis- 

 cussion as to the details, not only of the structure, but also of the 

 function of its elements. Tliis uncertainty has been due largely to 



