580 



degenerirten oder fragmentirten Kern vertreten kann. Für diese An- 

 schauungen ist natürlich die morphologisch-phylogenetische Deutung 

 des Centrosoms ohne Belang. 



Botan. Inst. d. böhna. Univ. m Prag. 



Nachdruck verboten. 



Hind Brain and Cranial Nerves of Acipenser^). 



By J. B. Johnston, 

 Instructor in Zoology in the University of Michigan, U. S. A. 



With 13 Figures. 



This paper contains a resume of the results of my work on the 

 hind brain of Acipenser rubicundus Le Seur, together with 

 some indication of the bearing of the results on our understanding of 

 the cranial nerves of vertebrates. The work, as that on the fore 

 brain, etc., recently published ('98), has been done by the method of 

 GoLGT on the brains of fishes 25 to 40 centimeters in length. The 

 entire brains have, in all cases, been treated by the silver method and 

 complete series of sections have been cut in different planes. A full 

 description of the minute structure of the medulla and the cerebellum, 

 and an examination of the literature will appear in my final paper. 



The accompanying figures are from a series of drawings made by 

 means of the Zeiss projection apparatus. The nerve elements are 

 drawn to scale either from the same sections as the outlines or from 

 neighboring sections. The drawings represent transverse sections 

 magnified 25 diameters. The position of the sections drawn is in- 

 dicated in Fig. 12, which is a sketch of the lateral aspect of the hind 

 brain of an adult fish, magnified 2 diameters. 



A. Medulla. 

 The medulla falls naturally into three parts: (1) the base of the 

 medulla, including the ventro-lateral tracts, the ventral horns, and 

 ventral roots, and corresponding to all that part of the cord lateral 

 and ventral to the dorsal horns ; (2) the centers for the nerves of the 

 V-VIII-lateral line group; (3) the centers for the nerves of the VII- 

 IX-X group. 



1) Work from the Zoological Laboratory of the University of 

 Michigan, Jacob Reighard, Director. 



