BRANCHIAL SENSE ORGANS IN ICHTHYOPSIDA. 127 
oral groove of Selachians, and also in the development of other 
fishes. Thus Marshall found in salmon embryos obvious 
diverticula of the oral mucous membrane, which stretched 
towards the nasal groove, but which later in the development 
disappeared. Smelling, argued Marshall, is only a modified 
breathing, and thus no violent physiological change is necessary 
to convert a gill into a smelling organ. 
Wiedersheim! himself formerly supported Marshall’s view, 
and pointed out that in Epicrium, and probably in other Gymno- 
pbiona as well, there are on either side two olfactory nerves, 
one dorsal and one ventral, the roots of the two being perfectly 
independent, and some little distance apart. He considered 
these roots to be homologous with the dorsal and ventrai roots 
of a spinal nerve, and that by their discovery the segmental 
rank of the olfactory nerve was established. But, as Prof. 
Wiedersheim has kindly informed me by letter, he has, since 
the appearance of Blaue’s paper (‘‘ Ueber Bau der Nasen- 
schleimhaut bei Fischen und Amphibien,” ‘ Archiv fir Anat.,’ 
1884), seen reason to change his views on this subject. 
The contents of this really important paper will be referred 
to shortly, and here I need only express my conviction that 
the results of Blaue’s work taken in conjunction with the light 
which I hope to throw on the development of the nose and its 
relationship to the other branchial sense organs, settle in a 
very definite and satisfactory manner the true homology of the 
nose. 
What has now to be demonstrated is that the nose is 
really a branchial sense organ, that is, the sense 
organ of anon-existent gill-cleft, and not a gill-cleft 
itself. 
It ought here to be mentioned that Hoffmann has already 
expressed a very similar view of the nature of the nose.? That 
is, he compares its whole development to that of the ear and 
* Wiedersheim, ‘ Anatomie der Gymnophionen,’ 1879, pp. 59, 60. 
? Hoffmann, “ Zur Ontogenie der Knochenfische,” ‘ Archiv f. Micros. Anat.,’ 
Bd. xxiii, p. 88. 
