STUDIES ON THE ELEMENTS OF THE CEN- 

 TRAL NERVOUS SYSTEM OF THE 

 HETERONEMERTINL 



THOS. H. MONTGOMERY, Jr., Ph.D. 



CONTENTS. PAGE 



I. Introduction 381 



II. Ganglion Cells , 384 



A. Cell I. 385 



B. Cell II. 386 



C. Cell III. 389 



a. Linetis 389 



b. Cerebratulus 395 



D. Cell IV (Cerebratulus) 398 



a. Disti-ibution 399 



b. Structure 402 



E. Comparison of the Ganglion Cells 403 



III. Nerve Tubules 405 



A. Cell III. 40s 



B. Cell IV 413 



IV. Neuroglia 416 



v. Dotted Substance of the Fibrous Core 420 



A. Linetis 420 



B. Cereh-atulus 425 



VI. Brain Commissures, Oesophageal Nerves , 426 



VII. General Conclusions 428 



VIII. Literature Cited 433 



IX. Explanation of Plates 438 



L Introduction. 



The present paper gives the results of investigations upon 

 the finer structure of the elements of the central nervous 

 system of Cerebratiihis lacteus (Verrill) and Linens gessereizsis 

 (O. F. Miill). It is more especially the structure of the ganglion 

 cells and of the nerve tubules which has received attention; but 



