The Reactions of the Vertebrate Embryo to Stimulation etc. 553 



prominent characteristic of the development of the nerve. In this 

 respect it does not differ essentially fiom a number of other nei ves, 

 for at several points in its course one may see elongated nuclei 

 lyiug- dose to the nerve although there are one or two Stretches 

 where it lies quite free in the mesenchymatous tissue. 



In the Glossopharyngeal the process of neurofibrillation has 

 made considerable advanee as compared with the earlier stage. 

 Many bundles unite the gauglion with the medulla and the indi- 

 viduai branches are well dififerentiated. The post- and praetrematic 

 branches contain, on a roiigh estimate, about an equal number 

 of tibrils. 



When the Vagus appears in the iield of the cross-sections the 

 arrangement of tibrils within the medulla is practically idcntical 

 with that of the Glossopharyngeal area. In both eases the largo 

 ventro- lateral group of cells is surrounded by many fibrils unitìng 

 to form bundles and entering the ganglia as roots. The total 

 number of such bundles Coming from the dorsal part of the medulhi 

 is markedly diminished as compared with the Trigeminus and Facial 

 centres. In the Vagus at this period, in contrast to the Glossopha- 

 ryngeal, neurofibrils may be deteoted at practically ali the points 

 where the formcr nerve is in contact with the epidermal thickening. 

 This fact has an important hearing upon the development of the 

 lateral-linc organs. AH branches of the Vagus includiug the Ramus 

 intestinalis are richly supplied with neurofibrils but ouly in rare 

 instances do they enter the organs which they ultimately supply. 



The Spinai uerves are in an advanced stage of neurotibrillation, 

 both ventral and dorsal roots are very prominent in the field as well as 

 the plexus formcd by their union, just ventral to the spinai ganglia. 

 From this plexus a large recurrent brauch is given off which supplies 

 the dorsal part of the myotorae. The ventral brauch follows the 

 inner bord of the myotome almost to its ventral end. In its course 

 it gives otf comparati veW few branches, and the majority of tliese 

 enter the myotome. The communicating branches with the collec- 

 tiun of cclls forming the sympathetic are well developed, the bund- 

 les of fibrils frequently split up forming a network about the cells 

 so that frequently in the piane of one section several cells unitod 

 by a common network nniy be made out. The cell-clumps and the 

 neurofibrils forming the sympathetic ganglia are already separated 

 by quite an interval from the ventral branches of the spinai nerves. 

 At the outer edge of these ganglia dose to the inner border of the 



