\. KifpFFKU, Cratiial Nerves of ^ crtehrates. zz^t^ 



zontal plane of the auditory vesicle, and arise at three sepa- 

 rate places, i.e., in the region of the trigeminus, acustico- 

 facialis and vagus. The epibranchial ganglia likew^ise emerge 

 descretely, and there is always one close above each gill 

 pouch. The part of the corresponding cranial nerve proceed- 

 ing over and outside the mesoderm secondarily unites with 

 these structures, and, indeed, the union with the lateral 

 ganglia is of such a nature that the rudiment of the nerve 

 itself swells into a new ganglion, the medial (neural ganglion. 

 Beard). From this union of the medial and lateral ganglia 

 proceeds the definitive ganglion (Hauptganglion) of the 

 cranial nerve concerned. The epibranchial ganglia take part 

 in the development of the terminal twigs of the cranial 

 nerves. In the separation of the lateral, as well as the epi- 

 branchial ganglia from the epidermis, there is nowhere 

 shown the rudiment of a sense organ. With the sole excep- 

 tion of the auditory vesicle, which is formed in the closest 

 proximity to the lateral ganglion of the acustico-facialis 

 region and is homodynamous with this lateral ganglion, all 

 these ganglia of both series are entirely independent struc- 

 tures, standing in no connection with principal sense organs. 



These were the results which I had reached. I had to 

 break ofi' these investigations, on account of lack of material, 

 at a stage in which the formation of the peripheral nervous 

 system is far from concluded. It was the moment of the 

 escape of the larvae (from the egg). I have since, with new 

 and more complete material, carried the work on further, 

 and extended it to the stage of larvae 4 mm. in length. At 

 the same time I discovered that my older material, upon 

 which the work cited had been based, contained gaps which 

 prevented me from arriving at a complete understanding of 

 the earliest beginnings of the cranial nerves. After interpo- 

 lation of the then lacking stages of development, it is neces- 

 sary to complete in many respects and partially correct my 

 earlier representation. 



The first rudiment I have sufficiently described and 



