228 JOHNSTON. [VOL. I. 



fishes hitherto is that of Van Gehuchten (-94) on the trout and 

 that of Sauerbeck ('96) on Elasmobranchs. Van Gehuchten 

 gives a single small figure of the end-branching of several 

 olfactory fibers, and Sauerbeck states that he has had a few 

 olfactory glomeruli and mitral cells impregnated, but gives no 

 figure. In the frog I have found stellate cells similar to those 

 in the granular zone of Acipenser, their axis cylinders directed 

 toward the fore-brain. Similar cells, but devoid of axis cylin- 

 ders, are shown in a figure copied by Edinger ('96b, p. 142) 

 from a paper by P. Ramon y Cajal (-94) which I have not seen. 

 The question of the interpretation of the various forms of nerve 

 cells in the olfactory lobe of vertebrates I am not yet prepared 

 to discuss. 



S. Ramon y Cajal ('96a) makes use of the mitral and granule 

 cells of the olfactory lobe to illustrate his principle that a nerve 

 cell gains a higher morphological development by the growth 

 of new processes, which by their position and direction set up 

 connections with a greater number of cells. Interpreted by 

 this statement, the large mitral cells of Acipenser present as 

 high a stage of differentiation as those of mammals, or higher. 

 The dendrites of these cells supply several, usually large glo- 

 meruli, into which a very large number of olfactory fibers enter. 

 Thus the number of cells with which they come into relation 

 is greater than in mammals. I have now shown also that non- 

 glomerular protoplasmic processes which were hitherto unknown 

 in lower vertebrates are present in Acipenser. With regard to 

 the granule cells, if centrally directed axis cylinders should be 

 found in higher vertebrates, all previous interpretations of them 

 will fall to the ground. Here, again, the presence of basal 

 processes goes to show that the morphological distinction 

 between nerve cells in fishes and mammals is not so great as 

 previous work has led us to suppose. 



B. The Fore-Brain. 



a. GENERAL DESCRIPTION OF NUCLEI AND FIBER TRACTS. - 

 In sections stained with methylene blue and acid fuchsin or with 

 haematoxylin there are to be seen several distinct collections of 



