758 ^^- J BEARD, 



olfactory nerve develops in precisely the same way as the cranial 

 segmental nerves: they arise at first from the upper part of the fore 

 brain, and gradually shift downwards, acquiring by so doing a second- 

 ary connection with the cerebral hemispheres, of which they are at 

 first completely independent ; and finally, the olfactory lobe or vesicle, 

 so far from being the earliest part to be developed, is actually the 

 last, no vestige of it appearing in the chick until the seventh day of 

 incubation, in the salmon till long after hatching, or in the dogfish 

 until stage of Balfour's nomenclature. 



HOFFMANN (48, p. 88) has also made some observations on the 

 olfactory nerve and organ, directed mainly to test Marshall's and 

 Dohrn's view of its gill-cleft nature. 



The description given by myself (36, p. 36) of the development 

 was as follows: — „the development of the nerve of the first segment 

 is practically that of a typical segmental nerve in which post- and 

 prae-branchial branches are aborted. 



The nerve grows down from the brain to a thickening of epiblast, 

 it fuses with this thickening, and a ganglion is formed at the point 

 of fusion. Even with the limited amount of material at the writer's 

 disposal, it can fairly well be shewn that the ganglion is formed from 

 the skin". 



For further particulars the reader is referred to the work cited, 

 and the above passage is only quoted in order that in what follows 

 the interpretations and extensions, so far as they differ from the former 

 account, may be obvious to the reader. 



Soon after the publication of my work. Dr. van Wlthe (55) 

 published some observations of his own, in order to refute my con- 

 clusions. His observations are correct, but as a matter of fact they 

 support instead of disprove my position. 



He remarks: — „Ich finde, dass der Olfactorius zu Anfang von 

 Balfour's Stadium 1 noch nicht vorhanden ist; er tritt erst zu Anfang 

 der Periode J auf, wann die vierte Kiementasche schon angelegt, aber 

 noch keine nach aussen durchgebrochene ist. Das Riechorgan und der 

 Nerv entstehen beide aus dem vorderen Neuroporus^). Der Olfactorius 

 entwickelt sich nicht aus der Nervenleiste, denn er tritt in einer Pe- 

 riode auf, wann dieselbe im Kopfe schon längst geschwunden ist; 

 auch ist er vom Anfang an mit der Haut in Verbindung und unter- 

 scheidet sich durch diese zwei Merkmale von allen übrigen dorsalen 



1} Not „aus dem vorderen Neuroporus" but in the region of it. 



