Johnston, TJic Brain of Petromyrjoii. 3 



origin from still more simple and generalized structures, and to 

 compare or connect them with the parts ot the spinal cord. In 

 all parts of the brain this attempt has resulted in the discovery 

 of more primitive conditions than have hitherto been known, 

 and it has been possible to trace the probable course of growth 

 and differentiation in certain brain centers from lower to higher 

 vertebrates. The chief significance of the present paper lies in 

 the fact that by the study of a lower vertebrate than the stur- 

 geon it carries this investigation to a fuller knowledge of facts 

 and to more certain conclusions. 



As in the study of the sturgeon brain, the work has been 

 done by means of Golgi sections with the aid of haematoxylin 

 preparations and dissections: The Golgi series were obtained 

 by treating the whole heads by the rapid osmium-bichromate 

 method and cutting complete series in the three conventional 

 planes. In some cases the ventral half of tne head was cut 

 away before hardening, but in all cases the ganglia of the cranial 

 nerves and (all or a sufficient part of ) the peripheral course of 

 the nerves was intact and impregnated so that the principal 

 nerve rami could be identified with certainty. The haematox- 

 ylin sections were also used in analyzing the roots and ganglia 

 and, although there are some points of extreme difficulty owing 

 to the small size of some of the nerve roots, it is thought that 

 in the ligiit of the recent work of Strong, Cole, Herrick and 

 Johnston both the central relations and the peripheral distribu- 

 tion have been correctly made out. No attempt has been made 

 to work out the distribution in detail, and the description of the 

 sense organs and cranial nerves is given a subordinate position 

 as an introduction to the discussion of theoretical questions 

 concerning the sensory centers of the medulla. 



It gives me pleasure to acknowledge my indebtedness to 

 Professor S. H. Gage of Cornell University and Professor J. 

 M. Reighard of the Univeisit>' of Michigan for hardened ma- 

 terial sent me during the past year. Through the courtesy of 

 the officials of the Marine Biological Laboratory at Woods HoU 

 I have been enabled to complete the work while occupying a 

 room for research in the laboratory during the past summer. 



