268 The Development of the Neuroglia 



more fibrillated appearance of the syncytium, the central canal resulting 

 fiom the collapse of the ventricle, and the thinning of the ependymal layer 

 (ep) due to the continued migration of the nuclei and the cessation of nuclear 

 ■division. In the dorsal horn (dh) the smaller variety of nuclei is more 

 numerous than elsewhere, i = ingrowths of pia visible because of slight 

 shrinkage of specimen; ??^!S = septum formed by fusion of internal limiting 

 membrane; » iz= first evidence of cell groups in ventral horn (vh); sp = begin- 

 ning of posterior septum; other letters ^ same as in previous figures, x 90. 



PLATE III. 



Fig. 9. Combined drawings from sections of same spinal cord as shown in 

 Fig. 8. Showing the increased filamentous appearance of the syncytium, the 

 further modified structure of the mantle layer (m), now studded with embry- 

 onic neuraxes, the form of the mid-ventral portion of the mantle layer (mv) 

 resulting from the forces of growth, and the ingrowths of mesodermal tissue 

 (j). Comparing the appearance of the section with the pictures obtained in 

 the same specimen by the silver method, the pia mater (p) is now positively 

 indicated in the more compact arrangement about the periphery of the 

 ■connective tissue syncytium (cs). Other letters 3= same as in other figures. 

 X 320. 



PLATE IV. 



Fig. 10. Combined drawings of lateral segments from sections of spinal 

 cord of a pig 55 millimeters long. Showing the finely fibrillated syncytium 

 "v/ith the radial arrangement maintained, the increased variation in the nuclei 

 •of mn, the increased complexity of the filaments at b, and the increased selec- 

 tiveness exerted by the filaments (r) upon the silver compound, x 300. 



Fig. 11. Combination drawing same as in Fig. 10, but from a pig of 70 mil- 

 limeters. Showing the beginning obliteration of the radial arrangement of the 

 syncytium and the beginning selectiveness of other than ependymal nuclei for 

 the silver. Z> = ' neuroglia cells" without nuclei; c^ cells probably contain- 

 ing nuclei; e^ filaments detached from the internal limiting membrane; other 

 letters == same as in Fig. 6. x 300. 



PLATE V. 



Fig. 12. Combination drawing from transverse sections of the spinal cord 

 ■of pig of 20 centimeters. Showing the condition of the syncytium, the first 

 appearance of neuroglia fibers and the probable nature of the " neuroglia 

 cells" of the silver method, a = neuroglia cell after the Benda method; a' 

 ^similar cell by the silver method; & and &' ^ non-nucleated neuroglia cells; 

 j"=rmass of the syncytium with silver deposit; (Z = free nuclei; e and f^ neu- 

 roglia fibers beginning to take the differential stain; 5 = seal-ring cells. 

 X700. 



Fig. 1.3. Area from transverse section from suckling pig of two tceeks. 

 Showing fully developed neuroglia fibers and fibers in process of transforma- 

 tion, and varieties of "neuroglia cells." a to fc:= neuroglia nuclei in various 

 stages; s = seal-ring cell, x ''^00. 



