Irving Hardesty 257 



variety. In fact, they probably do not begin to change till after they 

 are free. I can only explain the remaining types of neuroglia nuclei 

 as resulting from the shrinkage and possibly a deterioration of the vesicu- 

 lar type. First, there is a decrease in size {g. Fig. 13), resulting further 

 in a condensation of the chromatin {li), and finally a much smaller, 

 usually spherical, deeply staining form (A:). 



In the two adult hog specimens from Avhich I made preparations, the 

 small deeply staining forms of nuclei were somewhat more aliundant 

 than in the adult human. This may have been due to faulty technique. 

 In the adult especially a nucleus of the smallest type may be occasion- 

 ally seen which is apparently undergoing fragmentation. This phenom- 

 enon was described in the neuroglia of the elephant and further study 

 of the nuclei in the hog tends to strengthen the assumption that most of 

 the types are transition forms of the large vesicular variety; that having 

 to do with the growth and transformation of the syncytial protoplasm, 

 certain of the nuclei run a slowly terminating course, and finally suffer 

 gradual karyolysis, while others may maintain to take part in further 

 growth of the neuroglia. In the adult, vesicular nuclei are present with 

 the more deeply staining protoplasm about them, as well as without it. 



Of the various classifications of neuroglia nuclei in the literature, 

 Weigert's is, I think, more nearly correct. He describes them in the 

 human as (a) large vesicular; (b) small, deeply staining, and (c) transi- 

 tion forms between the two. Much more comjDlicated classifications 

 have been made (iVguerre, oo, and others). 



As to the nature of the neuroglia fibers, the conclusions originally sul)- 

 gested by Weigert are undoubtedly correct. The fibers cannot be re- 

 garded in any sense as processes or outgrowths of the cells, for they are 

 both morphologically and chemically different from the cell-protoplasm. 

 Furthermore, it may be added that, unlike cell-outgrowths, they often 

 pursue an unbroken course, not only through the entire domain of the 

 cell, but through the domain of several cells. In other words, they are 

 fibers distinct from the protoplasm but derived from it. They are 

 small, vary but little in thickness, and are of indefinite length. Their 

 chemical differentiation is seemingly the last stage of their development. 

 Unless the entire syncytium be considered as a cell (a nucleated mass of 

 protoplasm), the fibers are intra-syncytial in origin rather than either 

 intra- or extra-cellular. 



After medullation, and in the adult of all the forms I have examined, 

 there remains a peripheral excrescence, or cortical layer, of the syncy- 

 tium, which is unoccupied by the neuraxes of the spinal cord. In the 

 elephant (referred to as the " marginal veil ") it is considerably thicker 



