Irving Hardesty 239 



place, when used alone upon the stages it does act upon, it cannot be 

 trusted to tell the whole story. When it stains only the radial (thicker) 

 threads, as it usually does in the stages before these are broken up, the 

 picture obtained is highly suggestive of cell-processes, especially if the 

 precijpitation involves only the nuclei nearest the ventricle. Perhaps, 

 because of incomplete precipitation of the silver salt, few observers have 

 called attention to the smaller lateral branches or filaments uniting the 

 radially arranged " processes." Lenhossek, 91, notes such for the human 

 embryo, but found them only at the beginning of the processes. Eetzius 

 calls attention to abundant " Moosartige Aestchen/' and Kolster, 98, 

 describes especially strong lateral branches in the embryo salmon. Even 

 if seen very abundant and uniting the " cell-processes," none see in 

 these lateral filaments merely a modification of an earlier condition of 

 a continuous framework. In a comparative study of the ependyma, 

 including quite a number of animal species, Studnicka, 00, with other 

 methods than the silver, describes and pictures " ependymal cells " con- 

 tinuous with each other by numerous heavy connections which he calls 

 intercellular bridges. In some forms he especially describes these as 

 occurring near the ventricle or in the region of the nucleus of the 

 ependymal cell. His pictures show a perfect syncytium. Gierke, 85 

 and 86, though working with very inferior methods, in his illustrations 

 of the early stages of the marl-gerust shows a syncytium, though he 

 describes it in terms of anastomosing cells. 



The Proliferation, Migration and Distribution of the Nuclei. 



From the earliest stage, in which the embryonic spinal cord consists 

 of a single layer of cells, until even after the shape of the gray figure 

 is assumed, the nuclei show evidences of continual migration and change 

 of position. The general direction of the migration is radially outward 

 from the more thickly nucleated region nearer the ventricle or central 

 canal. The mantle layer, appearing early and seemingly as a peripheral 

 excrescence of the rapidly increasing syncytial protoplasm, is at first non- 

 nucleated. In pigs of about 10 millimeters, the stage when blood capil- 

 laries begin to grow in, a few nuclei may be found in the mantle layer, 

 but up to 5 centimeters all such belong exclusively to the blood capil- 

 laries and are therefore acquired from the outside. Up to 5 centimeters 

 in length the migration of the nuclei peripheralward is apparently 

 checked at the inner border-line of the mantle layer by the greater com- 

 plexity there in the arrangement of the filaments of the fibrillated proto- 

 plasm {h, Figs. 4, 7 and 9). Later, as the early arrangement is broken 



