THE OLFACTORY LOBES, FORE-BRAIN, AND 

 HABENULAR TRACTS OF ACIPENSER. 



A SUMMARY OF WORK ON THEIR MINUTE STRUCTURE! 



}. B. JOHNSTON, 



INSTRUCTOR IN ZOOLOGY, UNIVERSITY OF MICHIGAN. 



THE sturgeon of the Great Lakes, Acipenscr rnbicundus, Le 

 Sueur, grows to a maximum length of about two meters. In 

 my investigation I have used partly fish 25 to 40 cm. in length, 

 and partly the smallest of the fish taken at the fisheries, i to 

 i YZ meters in length. The greater part of the work has been 

 done by the method of Golgi, although I have used the ordinary 

 histological methods, and also methylene blue and acid fuchsin. 



The form and relations of the fore-brain and olfactory lobes 

 of Acipenser have been described and figured by Goronowitsch 

 ('88). The figures accompanying the present paper illustrate 

 the gross anatomy of these regions sufficiently well for an 

 understanding of their minute structure. All the figures are 

 from the brain of fishes 25 to 40 cm. in length. 



A. The Olfactory Lobe. 



In either transverse or longitudinal sections of the olfactory 

 lobe three zones are easily distinguished (Fig. i). These are, 

 from without inward : the zone of olfactory fibers (o.f.z.), the 

 zone of olfactory glorneruli (gl.z.}, and the granular zone or zone 

 of granule cells (gr.z.}. The bundles of olfactory fibers spread 

 out over the surface of the gray matter in such a way as to 

 form a cap whose thickness is greatest at the anterior end and 

 becomes nil near the junction of the olfactory lobe with the 

 fore-brain. This zone is made up of intercrossed bundles of 

 olfactory fibers with a small amount of connective tissue and a 

 few pigment cells between them. The glomerular zone is char- 



1 From the Zoological Laboratory of the University of Michigan, Jacob 

 Reighard, Director. 



