ox THE DEVELOPMENT AXD NATURE OF THE NEUEOGLIA. 



BY 



IRVING HARDESTY. 

 From the Hearst Anatomical Laboratory of the University of California. 



With 5 Plates. 

 CONTENTS. 



PAGE PAGE 



Introduction 239 Experiments with Digestion 258 



Material and Metliods 231 The Occurrence of Nerve Corpuscles, 



The Formation and Early Growth of or Seal-ring Cells, in the Central 



the Syncytium 233 Nervous System 260 



The Proliferation, Migration and Dis- Summary 262 



tribution of the Nuclei 239 Bibliography 264 



The Final Form of the Syncytium and Explanation of the Figures on Plates 



the Development of the Neuro- I-V 266 



glia Fibers from it 249 



Weigert's paper of 1895 aud the investigations stimulated by it have 

 led to the conclusion that the neuroglia as found in the adult nervous 

 system presents two general forms : 



First, the more plastic protoplasmic form. This occurs either as 

 masses of more or less modified protoplasm enclosing one or several 

 nuclei and having a more or less definite shape — " neuroglia cells " — 

 or it occurs in the more accumulated and somewhat different form of 

 the substantia gelatinosa. 



Second, it occurs in the form of the neuroglia fibers, which are in no 

 sense cell processes, but rather are both morphologically and chemically 

 dilferent from the protoplasm. However, they are derived from the 

 protoplasm, though the manner of their origin is not well understood. 



During a study of the neuroglia as found in the nervous system of 

 the elephant (Hardesty, 02), some appearances were noted which seemed 

 suggestive of the earlier form of the tissue and the processes by which the 

 neuroglia fibers are developed. The chief purpose of that paper was to 

 describe the adult form of the tissue as found in the spinal cord of the 

 elephant and to compare it with the more familiar appearances in the 

 adult human nervous system. In addition to this, however, attention was 

 called to evidences indicating (1) that the neuroglia tissue can in no 

 sense be looked upon as composed of independent, or even individual, 



American Journal op Anatomy. — Vol. III. 



