298 C. U. Aricns Kappers 



later, after the formation of the cochlea, in the axis of the cochlea (the 

 modiolus) so as to enter into the laminae osseae, almost reaching the sen- 

 sory epithehum of the car. So they are shifted fróm their original place 

 cióse to the oblongata, in the direction of the neuroepitelium from which 

 they receive their stimulus ^. 



Apart from this stimulo-petal cell-shifting ¡n th.efirst neiirone, the organ 

 of hearing exhibits still another example of the same in the second neurone. 



In Reptiles and in Birds, one of te nuclei, in which the cochlearis fibres 

 end, has a dorso-medial place in the oblongata, so dorsal so that it is 

 known as nuclens magnocelliilaris dorsalis VIII., of which the best des- 

 cription has been given by 5". Ramón y Cajal in his famous article on the 

 N. Octavus in birds -. Contrary in mammals, the greater part of this 

 nucleus has such a ventral place that it is called nucleus ventralis VIII. 



Minute comparative anatomical investigation of a large range of Rep- 

 tiles, Birds and mammals, convinced me that the ventral position of this 

 nucleus, on the outside of the oblongata is due to a gradual shifting of the 

 cells in the direction of the root by which they are stimulated, which 

 root, the R. cochlearis VIII, only acquires its greatest size in mammals 

 in consequence of the larger developement of the cochlea itself. Thus an 

 extrameduUary shifting here even occurs with cells of the second neurone. 



The influence of peripheral stimuli is still more evident in the shilting 

 of the part of the nervous system connected with the sense of sniell. 

 Here not only a large number of the second neurone cells (the mitral 

 cells) is subject to a considerable peripheral shifting, but the h-ainzvall 

 ¿/jf^makes a protrusion and is elongated into a stalk, the so-called olfac- 

 tory stalk. 



As this process in its essentials is intimately connected with the for- 

 mation of the eye-vesicle, I will discuss it a little further. 



' It might be supposed that this shifting had been effected bj»^ the growth of 

 the cells following the growth of the organ itself as they were inclosed in the tis- 

 sue of the modiolus, but then the question would arise, how this connection with 

 the tissue of the modiolus is accomplished, there being no foundation for it in the 

 primary «aniage» of these cells, ñor of the modiolus (cí. Streeter). The stimula- 

 tive relation between these ganglion cells and the neuroepithelium, enervated bv 

 them, is besides so intímate that their shifting or growth in that direction obvio- 

 usly must be ascribed to neurobiotactic causes. 



2 S. Ramón y Cajal: Les ganglions terminaux du nerf acoustiqíie diez les oiseaux. 

 Trabajos del Laboratorio de investigaciones biológicas, tomo vi, 1908. 



