228 BULLETIN: MUSEUM OF COMPAEATIYE ZOOLOGY. 



The glossopharyngeus is uow in fibrillar connection with the lateral 

 walls of the neural tube at a point behind eucephalomei'e YII. The 

 fibres from the ganglion cells of the vagus enter the nenral tube at a 

 point somewhat behind the point of origin of the glossopharyngeus. 

 The cells of the two nerve Anlagen, however, still appear continuous. 

 Posteriorly, and at the same level as the origin of the roots of nerves IX 

 and X, the neural-crest cells appear as a commissure {corns, d.) con- 

 necting the vagus Anlage with the ganglia of the dorsal spinal nerves 

 Ventrally the vagus divides into four mixed (post trematic) branches, 

 each of which inuervates the skin and musculature of a visceral arch, 

 and posteriorly is continued beneath the skin as the ramus lateralis 

 vagi along the medio-lateral line.-^ 



At this stage, I find the first evidence of the olfactory nerve (I) in 

 the form of connecting strands or fibres between the anterior lateral wall 

 of the forebrain (prosencephalon) and the thickened lateral epithelium 

 of the olfactory plate. The connection between the median portion of 

 the " Riechplatte " and the brain wall (neuropore) has disappeared at a 

 somewhat earlier period (8-9 mm.). According to Marshall ('78) and 

 Beard ('85) the olfactory nerve develops, as do the other dorsal cranial 

 nerves, from cells of the neural crest, and is therefore regarded by them as 

 a nerve morphologically comparable with the dorsal cranial nerves. The 

 evidence given by van Wijhe ('86^) and Hoffmann ('96), however, serves 

 in the opinion of these investigators to render this view improbable. 

 Van "Wijhe ('86% p. 680) states that "das Riechorgan und der Nerv ent- 

 stehen beide aus dem vorderen Neuroporus. Der Olfactorius entwick- 

 elt sich nicht aus der Nervenleiste, denn er tritt in einer Peri ode auf, 

 wann dieselbe im Kopfe schon langst geschwuuden ist ; auch ist er von 

 Anfang an mit der Haut in Yerbindung und unterscheidet sich durch 

 diese zwei Merkmale von alien iibrigen dorsalen Nervenwurzeln. Der 

 Ptiechnerv entsteht also erst nach dem Acranienstadium und in Ueberein- 

 stimmung damit ist seine Abwesenheit beim Ampliioxus." 



Confirmatory of this view is the evidence given by Hoffmann ('96, 

 p. 272) that "der Eiechnerv fehlt [in Squalus] aber bis zu diesem Ent- 

 wicklungsstadium [10-12 mm.] noch vollstandig und erst bei Embi-yo- 

 nen, welche eine Lange von 13|-14 mm, erreicht haben, beginnt er sich 

 anzulegen. Bis zu dieser Periode liegt die Riechgrube der Medullar- 



1 Squalus possesses no r/orso-lateral line nerve corresponding with that of 

 Cyclostomata, Dipnoi, and Ganoidei. I also find no evidence in Squalus such as 

 that found by Miss Piatt ('94) in Necturus, to show that there once existed a ventro- 

 lateral line in Vertebrates. 



