Irving Hardesty 245 



germinal cells are none other than undiiferentiated dividing elements, 

 that the products of their division may develop either into neurones or 

 neuroglia, or may further divide and still be indifferent. In other words, 

 both the neuroblasts and spongioblasts are derived from the germinal 

 cells. Paton, oo, working with pig material, agrees with Schaper in this 

 assertion. In one of his later discussions. His, oi, refers to Schaper's 

 paper and, while not wholly admitting his position, calls attention to 

 the general definition of " germinal cell " : A young element in a state 

 of division, as yet morphologically undifferentiated (in status nascens), 

 which by its globular form and bubble-like appearance is easily distin- 

 guished from its surroundings. 



In the spinal cord of the pig it is true that up to a certain stage all 

 the products of the mitoses are so nearly identical that, morphologically, 

 no trustworthy distinctions can be made among them. On the other 

 hand, however, it may not be just to judge them indifferent upon wholly 

 morphological grounds. A neurone, for example, to be distinguished 

 as such, must first acquire certain characteristic features and, while these 

 features are certainly acquired by elements seemingly similar in every 

 respect to those which acquire other features, it is difficult to say whether 

 they do not possess, from the first, the peculiar properties necessary for 

 the acquirement, or whether such properties result in reactions to influ- 

 ences of later environment. It is, I think, certain that collectively the 

 dividing nuclei known as germinal cells give rise to both embryonic 

 neuroglia and to nervous elements, and with the ordinary technique one 

 can but agree with Schaper that the products of the divisions are at first 

 ■ indifferent. 



Paton, 00, finds in the brains of embryo pigs, except in the very 

 earliest stages, two types of germinal cells ; one large, having protoplasm, 

 and the other smaller with no protoplasm about it. Both of these he 

 says give rise to indifferent elements. Hamilton, oi, also describes large 

 and small types in the white rat, and ascribes to the larger the origin 

 of neurones and to the smaller the origin of neuroglia. In my prepara- 

 tions of the spinal cord of pig embryos, it seems to me that the amount 

 of protoplasm about a dividing nucleus and, indeed, the apparent size 

 of the nucleus itself, depends upon its position in the syncytium. If 

 the dividing nucleus occurs in the ventricular border of the ependymal 

 layer where the absence of nuclei allows a greater relative abundance 

 of protoplasm, it will of necessity be enclosed by a greater amount. If 

 the division occurs among the very compactly arranged nuclei of the 

 ependymal layer, which is thick during the active period of mitosis, the 

 nucleus will be surrounded by much less protoplasm, or often apparently 



