262 Joi KNAL OK Comparative Neurology. 



from the dorsal brain-plate and border respectively at any 

 time give up their connection with the dorsal region of the 

 brain. I assume this separation only for the region of the fore - 

 brain., where the rudiments also possess secondarily no 

 connection with this region of the brain, but are united 

 with the trigeminus and the mid-brain respectively. Be- 

 hind this it does not occur, at least not up to the point of 

 time when the formations of ganglia from epidermis begin 

 and come forth in connection with the roots of the branchial 

 nerves. With this question is bound up the other question of 

 the final fate of the dorsal brain-plate. Do its cells advance 

 in a body laterad and ventrad, or a middle portion of the cells 

 of the plate remain in loco, while these cells intercalate 

 themselves in the epithelial covering of the neural tube? 

 According to my observations the latter takes place. A great 

 part of the plate is applied to the formation of the peripheral 

 nerves, but the remainder appears wedged in between the 

 cells of the roof of the brain without the interruption of the 

 connection wnth the peripheral parts. 



I do not propose to discuss the histogeny of the nerves in 

 this place, since the details are still not clearly enough 

 established to admit of generalizations; but I may devote 

 space for the view to which the embryo and the youngest 

 larval stages of Petromyzon have led me. None of my 

 observations contradicts the view, but rather everything 

 indicates that the fibrill^e arise as processes of cells, but not 

 merely from cells of the ganglia and central organ but also 

 from those cells which, ranged in chains, form the first rudi- 

 ments of peripheral nerves. This being accepted, it appears 

 to me, further, most probable that the growth of the fibrillas 

 in the dorsal nerves extends in both directions, centripetal as 

 well as centrifugal. Thus, when the rudiments have attained 

 the stage of formation at which they display fibrillge along 

 with the cells, the cells appear moved apart from each other, 

 and at both ends, the central as well as the peripheral, pro- 

 ceeding forth in fine filaments. 



