Anatomy of the Brain of Bdellostoma Donibeyi 7 



Cajal sections fine fibers running towards these cells divide, on reaching 

 them, into two or more fibrils which apply themselves closely to the 

 surface of the cell. 



We have not been able as yet to identify these fibers. In the sections 

 where they appear they are impregnated in a somewhat different manner 

 from the ends of the entering fibers, and as yet we have not succeeded 

 in tracing them into definite bundles. 



When the small cells are studied in Golgi sections they are seen to 

 belong to both the spindle and multipolar types of cells. Fig. 31 shows 

 two small cells lying in the dorso-cephalic part of the nucleus. The left 

 cell is the more mesial of the two and belongs to the spindle-shaped 

 variety. The fiber running mesad is cut off close to the cell; the other, 

 running latero-ventrad, forks a little beyond the cell, giving rise to 

 three others, all of which run more or less laterad. The one that runs 

 farthest forks again, one of its subdivisions being a fine-beaded fiber. 

 None of the prolongations of this cell run beyond the acusticus nucleus. 

 The other cell is of the multipolar variety, giving off two very fine and 

 two heavy prolongations. The two fine fibers run laterad and mesad. 

 Of the two heavy ones the shorter runs ventrad, the longer dorsad; this 

 latter, about half way of its lengih from the cell, becomes very fine and 

 beaded with round or oval beads. It penetrates among the fibers of the 

 fasciculus communis that overlie the acusHcum. Figs. 33 and 35 show 

 small cells lying in the ventro-mesial part of the nucleus about midway 

 of its length, close to the fibers of the great ventral commissure. Fig. 

 33, which likewise sends its axone into the ventral motor column of its 

 own side, is a tri-polar cell, having, beside the axone, one short fine 

 fiber, and one stout one that subdivides later into two fine ones. Fig. 

 35 is a spindle cell whose mesial prolongation bifurcates, sending one 

 branch dorsad, the other ventrad. The dorsal fiber is cut off close to 

 its starting point, the ventral one divides again, giving off a fine- 

 beaded fiber running mesad, and the axone that runs ventrad, and pierces 

 through the ventral commissure to end in the ventral motor column 

 of its own side. 



The Large Cells. — The large cells are few in number compared to the 

 small ones. Occasional ones are found all through the nucleus and a 

 large group of them occurs in the ventral part caudad of the middle. 

 These large cells are generally elongated in shape with large nuclei. 

 Sometimes they are spindle-shaped, as in Fig. 34, sometimes tri- or mul- 

 tipolar (Figs. 36 and 37). These cells, whatever their form, usually 



