NERVES OF THE DOGFISH 297 



ment of the nervus terminalis in Selachians (Acanthias, Raja, 

 Torpedo), concludes that the olfactory nerve develops out of and 

 supplants a primary ganglionic nerve of the olfactory vesicle. 

 The nervus terminalis of selachians, according to him, is but a 

 persisting remnant of the primary nerve. The primary olfactory 

 nerve is a derivative of the olfactory placode. The secondary 

 olfactory nerve (olfactory nerve proper) is then but a derivative 

 of the nervus terminalis. Brookover agrees with Belogolowy, 

 except that he does not see any need or propriety in calling the 

 ganglion a primary olfactory ganglion. 



To the account given by Locy ('03) of the nervus terminalis 

 of Squalus acanthias the writers have nothing of importance to 

 add. In the words of that writer: 



Starting deep in the median furrow, it passes forward across the 

 anterior surface of the forebrain; it then curves in the angle formed by 

 the union of the olfactory tract and the forebrain, and finally passes 

 along the inner margin of the tract, to reach the median division of the 

 fila olfactoria. It crosses this obliquely and enters the fissure between 

 the two divisions of the fila. 



For a review of the literature relating to the nervus terminalis, 

 the paper by Larsell ('18) should be consulted. 



To quote further from Locy ('99): "The olfactory nerve in 

 selachians has for a long time been represented as double, but 

 very little has been said about it in descriptions of figures or in 

 texts." Locy ('99, '03) has described the development of the 

 olfactorius in Squalus acanthias, showing that in its earlier stages 

 it is distinctly double. Those who have figured the double char- 

 acter of the olfactory nerve in selachians have for the most part 

 concerned themselves with the olfactory bulb. Miklucho-Maclay 

 ('70), in many excellent figures of the brains of various selach- 

 ians, has shown very plainly that the olfactory bulb is distinctly 

 double. Locy draws a sharp distinction, as most of his prede- 

 cessors have not done, between the olfactory fila (olfactory nerve) 

 and the olfactory bulb and tract. 



As Locy observes in the 150-mm. stage of Squalus, a distinc- 

 tion externally between bulb and tract can hardly be made. In 

 section, however, there may be distinguished in the olfactory 



