ScHAPER, Structure of Selachian Cerebellum. 5 



Kornerschicht hin, einen Axencylinder senden, der sehr bald in 

 die horizontale, resp. tangentiale Richtung umbiegt ; nach aus- 

 sen ragen armleuchterartige Dentritenfortsatze, doch sind diese 

 nicht so reich verzweigt wie bei hoheren Vertebraten, wie auch 

 schon bei den Teleostiern ScJiaper sie abgebildet hat." The 

 figures given by Sauerbeck are, in consequence of their small 

 scale, but little adapted to reproduce the characteristics of these 

 cells. I have therefore again represented two typical forms of 

 Purkinje cells in Plate I, Figs, i and 2. We see from these 

 that the size and form of the cell-body, as well as the magnitude 

 and arrangement of the protoplasmic processes, are subject to 

 considerable variation. This is correlated in part with the very 

 variable thickness of the molecular layer ; we meet the more 

 massive and coarser type (Plate I, fig. i) mostly in the more 

 strongly developed portions of the molecular layer, the smaller 

 and more delicate type (Plate I, fig. 2) mostly in the thinner 

 regions of this layer. As Sauerbeck rightly remarks, the 

 protoplasmic processes are not so richly branched as is usually 

 the case among the higher vertebrates and one can compare 

 them in this respect with those of the bony fishes, as some time 

 ago (5) described and figured by me. They are distinguished, 

 however, even from the latter by a still more sparse arborization 

 and their less straight, irregular course to the surface. One 

 could say they stand upon a still lozver plane of development tJian 

 those of the bony fishes and display throughout life an embryonic 

 condition of the hotno logons cells of the higher vertebrates. Like 

 the dendrites of all Purkinje cells, these are provided with a 

 thick covering of very fine spines and usually tend to terminate 

 with a slight thickening. 



Concerning the axis-cylinder, this also presents certain note- 

 worthy peculiarities. With respect to their course, they be- 

 have differently according as they come from cells which have 

 a granular layer beneath them or from such as, in the absence 

 of the granular layer, lie close to the memb^ana lirnitans in- 

 terna. (See text-figure, p. 4). In the latter case (Plate I, fig. 

 i) the axis-cylinder is naturally compelled, soon after its origin 

 from the under pole of the cell, to bend laterally and proceed, 



