456 '. EMBRYOLOGY. 



I desire to lay particalar stress upon the observations of Dohen and VAN" 

 WijHB, because they harmonise with the theoretical views which I have 

 formed as the result of investigations on Invertebrates. As I have in several 

 articles endeavored to establish, protoplasmic connections of the cells are the 

 foundation out of which the nerve-fibrillffi are developed. The formation of a 

 specific nervous system is preceded by a protoplasmic union of cells, which is 

 effected at a, time when the central and terminal nervous organs are still in 

 the immediate vicinity of each other. 



The dorsal roots become visible somewhat later than the ventral 

 roots ; there are formed fibrillse which unite the upper [dorsal] end 

 of the spinal ganglion with the side of the'Spinal cord. 



(2) GoTTE, Semper, Wijhe, Hoffmann, and Beard have made 

 concerning certain nerves the noteworthy statement — which has been 

 called in question: by some observers (Balfour, Sagemehl) — that the 

 epidermis participates in their formation. In-Amphibian larvae 

 and Selachian embryos the posterior end of the nervus lateralis vagi 

 in process of development is completely fused with the primitive 

 epiderm,is, which is thickened in the lateral line (fig. 262 ?iZ). Some- 

 what farther forward the nerve is detached but still lies in close 

 contact with the primitive epidermis, whereas in the vicinity of the 

 head it is situated deeper and lies between the muscles. At the 

 places where the nerve has become separated from the primitive 

 epidermis, it remains in connection with the fundaments of the 

 lateral organs by means of fine accessory branches only. Similar 

 observations have also been made in the case of many of the branches 

 of other cranial nerves in Selachian embryos. Wijhe sees, for 

 example, a short branch of the n. facialis near its emergence from 

 the brain so fused with a thickened portion of the epidermis composed 

 of cylindrical cells, that it is impossible to say whether at the place 

 of transition the cell-nuclei belong to the nerve or to its terminal 

 organ. During a more advanced stage the older part of the nerve 

 is detached from the terminal organ, sinks into the depths, becoming 

 separated from the skin by ingrowing connective tissue, and remains 

 united with the terminal organ only through fine accessory branches. 

 The persistently growing younger end of the nerve still continues to 

 be cpnnected with the epidermis. 



Also in the case of the higher Vertebrates similar conditions have 

 oeen observed by Beard, Froriep, and Kastschenko. They find 

 the ganglionic fundaments of the facialis, glossopharyngeus, and 

 vagus at the dorsal margin of the corresponding visceral clefts for a 

 long time broadly fused with the epithelium, which is thickened and 

 has become depressed into a pit. In these connections they discern 



